Bismuth vanadate pigments comprising a doped core coated with an oxidic coating

Abstract

A bismuth vanadate pigment comprising a bismuth- and vanadium-containing core doped with one or more of magnesium, calcium, aluminium and phosphorus, the doped core being coated with an oxidic coating comprising one or more of magnesium, calcium, aluminium and phosphorous.

Description

[0001] Bismuth vanadate pigments comprising a doped core coated with an oxidic coating

[0002] The present invention relates to bismuth vanadate pigments comprising a bismuth- and vanadium-containing core doped with one or more dopants and coated with one or more metal phosphates, to a process for preparing same, for bismuth vanadate pigments obtainable or obtained by said process, and to the use of said bismuth vanadate pigments is specific applications.

[0003] When yellow colorations of good performance properties are desired, lead chromate pigments are often used. However, due to environmental restrictions and toxicity concerns, the use of chromate- containing pigments as well as lead-containing pigments is decreasing. As a substitute, other inorganic yellow pigments are used. Bismuth vanadate pigments are well known as suitable yellow pigments. In particular, they are highly valued due to their low toxicity and good color properties in different applications like coatings, printing inks and plastics. However, while bismuth vanadate pigments exhibit high thermal stability, chemical resistance and weatherfastness, the chroma and color strength is inferior to some yellow organic pigments. Therefore, in some bismuth vanadate pigments, some of the metal and / or oxygen atoms are replaced by other metals and / or non-metals to further improve the chroma and color strength as well as the weatherfastness and thermal stability. Moreover, bismuth vanadate pigments are provided with stabilizing coatings. These coatings especially improve their thermal stability, weatherfastness and chemical resistance.

[0004] The color strength of a pigment refers to its ability to impart color when mixed with other substances, like paints, inks, or plastics. It is a measure of the intensity of the color imparted by the pigment and of the depth of the color. Thus, a pigment with high color strength will strongly influence the color of a mixture, even in small quantities. This property is important for manufacturers and anyone working with colored materials as it determines how much pigment is needed to achieve the desired color effect. Typically, the color strength in pigments is measured using a few different methods:

[0005] Tinting Strength: This involves mixing the pigment with a white base (such as titanium dioxide) to see how much white it takes to reach a specific shade. A pigment with high color strength will require less amount to reach the same shade.

[0006] Spectrophotometry: This is a more precise scientific method that measures how much light is absorbed, transmitted or reflected by the pigment at different wavelengths.

[0007] Visual Assessment: Skilled colorists can often judge the color strength of a pigment by eye, comparing it to reference standards.

[0008] According to the present invention, the color strength is measured as described in Reference Example 3 herein. However, the color properties of recent bismuth vanadate pigments are still inferior to some yellow organic pigments when it comes to chroma and color strength, which prevents their use as a substitute for lead chromate pigments to some extent. Therefore, it is an object of the present application to provide a yellow bismuth vanadate pigment exhibiting superior color strength while maintaining a high chroma. A bismuth vanadate pigment has been developed which exhibits the desired performance characteristics. The pigment is comprised entirely of elements which are either free from or with greatly reduced toxicological concern.

[0009] Doping of the bismuth vanadate core may enhance light stability and weathering of bismuth vanadate pigments. Special coatings can also enhance pigment stability for special applications but often have the undesirable effect of reducing color strength. US 9,868,860 emphasizes, however, that pigments exhibiting a high color strength for more advanced applications cannot be achieved by combining doping with coating. According to the present invention, however, higher color strength can be generated by a specific combination of doping the bismuth vanadate core of a pigment and adding a coating, especially a metal phosphate coating, when compared to other yellow bismuth vanadate pigments. Advantageously, higher or equal color strength can be produced while using less pigment, making the system more sustainable for the environment by reducing the amount of pigment introduced into the waste stream, i.e. the weight percentage of the chromophore BiVC is decreased in the pigment while maintaining or enhancing the color strength.

[0010] US 6,423,131 refers to stabilizing coatings consisting of metal fluorides which also may be combined with metal oxide layers forming an oxyfluoride coating. These coatings improve the stability and weatherfastness of the pigments also show good color properties, especially high chroma and lightness. However, there is no indication of how to get stable bismuth vanadate pigments with high color strength. While during the synthesis calcium hydroxide, zinc oxide and phosphoric acids are used, a strict combination of doping and coating is not mentioned. In addition, some fluoride compounds show toxic behaviour. In contrast to this teaching, the present application only relates to non-toxic elements or compounds.

[0011] US 5,123,965 refers to stabilizing coatings consisting of several metal phosphates to increase the stability against attack by hydrochloric acid. Mixtures with ammonium fluoride are also mentioned. As a basis (Bi,Ca)(V,Mo)O4 is used as it is a more reddish bismuth vanadate pigment. The coating only enhances the stability against an attack of hydrochloric acid which is not in focus of the present application.

[0012] US 5,536,309 refers to a doped bismuth vanadate. Several elements like Ca, Zn, Mg, Si, Li and Al are used. It is mentioned that the silicon-containing bismuth vanadate pigments have sufficient thermal stability and no subsequent coating is necessary to further improve the thermal stability and chemical resistance. This patent solely refers to stable bismuth vanadate pigments and gives no indication how to achieve both stable and high color strength pigments.

[0013] US 9,868,860 refers to a doped bismuth vanadate similar to US 5,536,309. The list of dopants is extended with elements like Ce, Sr, Ba, Mo and Zr. It is mentioned that the pigments, especially doped with at least Mg, Al and Ca, are sufficiently stable with respect to heat, light or chemical resistance. US 9,868,860 represents a teaching away from the present application in that it shows that high color strength pigments with enough stability can be generated by avoiding an extra coating of the pigments which would reduce color strength. Further, the color strength reached is not sufficient for demanding applications.

[0014] CN 106349756 A refers to a yellow inorganic pigment with the formula BiaAbBcCdO4 referring to a highly altered BiVCU yellow pigment. While A are several dopants like Si, Ti, Ge, Zr, B, Al, Ga, In or Tl, the VO43' construct is further altered by doping with Nb, Ta, Mo and / or W on the B and C site. This is clear since the ionic charge of V is +5. The ionic charge of Nb, Ta, Mo and W is +5 or +6 and therefore it is highly unlikely that those elements will substitute Bi in the crystal lattice having an ionic charge of +3. Thus, the application refers to highly altered BiVCh crystal lattice to such an extent that one can argue that is more likely to be a Bi(V, Nb, Ta, Mo, W)O4 rather than BiVC . Although several coatings are mentioned, there is neither a color strength given nor mention of how to achieve products which are stable and have high color strength.

[0015] There remains a need for bismuth vanadate pigments with high color strength for more advanced applications.

[0016] Surprisingly, it was found that such bismuth vanadate pigments can be provided by specifically doping the bismuth vanadate pigment core and, after doping, coating the doped core with an oxidic coating. Said doping may comprise doping with one or more of magnesium, calcium, aluminium and phosphorus, and, optionally additionally, with one or more of strontium, barium, boron, iron, and zinc. Said coating may comprise coating with an oxidic coating comprising one or more of magnesium, aluminium, calcium and phosphorous. It may be conceivable that additionally, zinc, iron, boron, strontium and barium may be comprised in the oxidic coating. Thus, the present invention describes a bismuth vanadate pigment comprising a bismuth- and vanadium-containing core doped with one or more dopants and coated with one or more metal phosphates.

[0017] In particular, it was found that such bismuth vanadate pigments can be provided by doping the bismuth vanadate pigment core with one or more of magnesium, calcium, aluminium and phosphorus, and, after doping, coating the doped core with an oxidic coating comprising one or more of magnesium, aluminium, calcium and phosphorous.

[0018] Therefore, the present invention relates to a bismuth vanadate pigment comprising a bismuthand vanadium-containing core doped with one or more of magnesium, calcium, aluminium and phosphorus, the doped core being coated with an oxidic coating comprising one or more of magnesium, calcium, aluminium and phosphorous.

[0019] According to the present invention, it is preferred that the bismuth vanadate pigment consists of the bismuth- and vanadium-containing core doped with one or more of magnesium, calcium, aluminium and phosphorus, the doped core being coated with an oxidic coating comprising one or more of magnesium, calcium, aluminium and phosphorous. According to the present invention, it is more preferred that the bismuth vanadate pigment consists of the bismuth- and vanadium-containing core doped with one or more of magnesium, calcium, aluminium and phosphorus, the doped core being coated with an oxidic coating consisting of oxygen, one or more of magnesium, calcium, aluminium and phosphorous, and optionally hydrogen.

[0020] Preferably, the bismuth- and vanadium-containing core according to the present invention is doped with two or more of magnesium, calcium, aluminium and phosphorus, preferably with three or more of magnesium, calcium, aluminium and phosphorus, more preferably with magnesium, calcium, aluminium and phosphorus.

[0021] Further preferably, the oxidic coating comprises two or more of magnesium, calcium, aluminium and phosphorous, preferably three or more of magnesium, calcium, aluminium and phosphorous, more preferably magnesium, calcium, aluminium and phosphorous.

[0022] Thus, according to the present invention, bismuth vanadate pigment are especially preferred comprising a bismuth- and vanadium-containing core doped with magnesium, calcium, aluminium and phosphorus, wherein said doped core is coated with an oxidic coating comprising magnesium, aluminium, calcium and phosphorus.

[0023] According to the present invention, it is preferred that the oxidic coating comprises one or more of magnesium oxide, magnesium phosphate, calcium oxide, calcium phosphate, aluminium oxide and aluminium phosphate. In other words, the metals used, i.e. the one or more of magnesium, calcium and aluminium are present in the oxidic coating preferably either as phosphate and / or as oxide.

[0024] Preferred pigments of the present invention are characterized by a composition according to formula (I) Bi MgaAlb CacVd Pe Of (I) wherein

[0025] 0.025 < a < 0.20; preferably 0.025 < a < 0.15; more preferably 0.025 < a < 0.10;

[0026] 0.025 < b < 0.20; preferably 0.025 < b < 0.15; more preferably 0.025 < b < 0.10;

[0027] 0.045 < c < 0.30; preferably 0.045 < c < 0.28; more preferably 0.045 < c < 0.26;

[0028] 0.50 < d < 2.0; preferably 0.60 < d < 1.9; more preferably 0.65 < d < 1.8; wherein e and f denote the number of phosphorous and oxygen atoms for satisfying the valence requirements of formula (I).

[0029] Wirth regard to formula (I), it is preferred that 0.1 < e < 0.5; more preferably 0.13 < e < 0.45; more preferably 0.15 < e < 0.4.

[0030] Typically, the pigments of the present invention will differ in the chemical composition of the core and the exterior coating. Therefore. The above-described composition according to formula (I) is to be understood as the total composition of the pigment.

[0031] In the pigment according to the present invention, bismuth is generally present as Bi(III) and vanadium is generally present as V(V); however, vanadium may also be present both as V(V) and V(IV) wherein V(V) is provided by employing suitable V(V) compounds and V(IV) is provided by employing suitable V(IV) compounds in the preparation process. By way of example, a suitable V(IV) compound is vanadium(IV) oxy sulphate. Generally, the elemental ratio V(IV) : V(V) in the pigment of the present invention is in the range of from 0:1 to 0.3:1, preferably in the range of from 0.01:1 to 0.3:1, more preferably in the range of from 0.05:1 to 0.25:1.

[0032] Commercially available bismuth vanadate pigments sometimes contain molybdenum to increase the chroma value C* of the pigment, to shift the hue angle or to achieve a specific crystal modification of bismuth vanadate. Silicon is sometimes used to enhance the dispersibility, color strength, and / or stability. Surprisingly, according to the present invention, it was found that neither molybdenum nor silicon is necessary to achieve a high color strength, and thus, with regards to the preparation process of the pigments according to the present invention, neither molybdenum containing compounds silicon containing compounds are employed.

[0033] Therefore, the pigment of the present invention is preferably characterized by a silicon content of at most 2000 weight-ppm, preferably at most 1500 weight-ppm, more preferably at most 1000 weight-ppm, calculated as elemental Si, wherein more preferably, the pigment is substantially free of silicon. The term “substantially free of silicon” as used herein is defined as “not containing any free or added silicon but possibly containing trace amounts in the form of impurities”.

[0034] Therefore, further, the pigment of the present invention is preferably characterized by a molybdenum content of at most 1500 weight-ppm, preferably at most 1000 weight-ppm, more preferably at most 800 weight-ppm, calculated as elemental Mo, wherein more preferably, the pigment is substantially free of molybdenum. The term “substantially free of molybdenum” as used herein is defined as “not containing any free or added molybdenum but possibly containing trace amounts in the form of impurities”.

[0035] Still further, the pigment of the present invention is preferably characterized by a zinc content of at most 2000 weight-ppm, preferably at most 1500 weight-ppm, more preferably at most 1000 weight-ppm, calculated as elemental Zn, wherein more preferably, the pigment is substantially free of zinc. The term “substantially free of zinc” as used herein is defined as “not containing any free or added zinc but possibly containing trace amounts in the form of impurities”.

[0036] Preferably, the pigment of the present invention is in the form of particles. While there is no specific restriction to the particle size of the pigment of the present invention, it is preferred that the particle size is in the range of from 0.2 to 3.0 pm, more preferably from 0.25 to 2 pm, more preferably from 0.3 to 1.4 pm, the particle size being determined as described in Reference Example 1.

[0037] According to the present invention, the pigments preferably exhibit a color strength of at least 105 %, more preferably at least 107 %, more preferably in the range of from 107 to 140 %, more preferably in the range of from 110 to 140 %, more preferably in the range of from 120 to 140 %. The percentages as indicated are given relative to a reference material RM; reference is made to the respective definitions according to Reference Example 3 herein.

[0038] Bismuth vanadate pigments are pigments exhibiting a hue angle h° which is in the yellow region. Some distinctions can be made between a more reddish or a more greenish yellow. Typically, hue angle h° values of at least 90 are preferred. Values of h° of from 90 to 100 typically correspond to a greenish yellow. Further, bismuth vanadate pigments are often used to colourize different matrices, such as plastics and coatings. The chroma value C* of the bismuth vanadate pigment defines the brilliance and intensity of the color and therefore determines which RAL color standards (the RAL color standard is maintained by the RAL “Deutsches Institut fur Gtitesicherung und Kennzeichnung”) can be realized using the pigment; generally, the higher the chroma value C*, the more RAL colors can be realized. However, increasing the chroma value C* without changing other color properties, like the hue angle h°, is quite challenging. Therefore, a high chroma value of C* > 90 is preferred. Still further, a lightness value L* value of > 80 is preferred to achieve bright colours. It was found that the pigments of the present invention, in in addition to the extremely advantageous high color strength, exhibits all of these preferred characteristics.

[0039] Therefore, the pigments of the present invention preferably exhibit a hue angle h° of at least 90, more preferably in the range of from 90 to 95, more preferably from 91 to 95, determined as described in Reference Example 2 herein.

[0040] Further, the pigments of the present invention preferably exhibit a chroma value C* of at least 90, more preferably at least 91, more preferably at least 92, more preferably in the range of from 92 to 97, more preferably in the range of from 92 to 96, determined as described in Reference Example 2.

[0041] Still further, the pigments of the present invention preferably exhibit a lightness value L* of at least 80, more preferably at least 81 , more preferably at least 82, more preferably in the range of from 82 to 87, more preferably from 82 to 86, determined as described in Reference Example 2.

[0042] Thus, according to the present invention, the pigments preferably exhibit a a hue angle h° of at least 90, a chroma value C* of at least 90, and a lightness value L* of at least 80; more preferably exhibit a a hue angle h° in the range of from 90 to 95, a chroma value C* of at least 92, and a lightness value L* of at least 82; more preferably exhibit a a hue angle h° in the range of from 91 to 95, a chroma value C* in the range of from 92 to 97, and a lightness value L* in the range of from 82 to 87 ; more preferably exhibit a a hue angle h° in the range of from 91 to 94, a chroma value C* in the range of from 92 to 96, and a lightness value L* in the range of from 82 to 86.

[0043] Especially preferred pigments of the present invention exhibit a color strength in the range of from 130 to 140 %, a hue angle h° in the range of from 93 to 95, a chroma value C* in the range of from 95 to 96, and a lightness value L* in the range of from 85 to 86.

[0044] According to the present invention, in particular described in the example section herein, it was surprisingly found that while the presence of the oxidic coating is necessary for achieving the desired properties of the pigment, there is a clear tendency that the lower the amount of the one or more, preferably two or more, more preferably three or more, more preferably all of Al, Ca, Mg and P comprised in the oxidic coating according to step (ii), the higher the (improved) color strength of the pigment. In particular, for the elemental ratio R of the one or more, preferably two or more, more preferably three or more, more preferably all of Al, Ca, Mg and P comprised in the oxidic coating, relative to the amount of Bi and V, (Bi+V), comprised in the doped core, it is preferred that 0 < R < 0.4, more preferably 0 < R < 0.35, more preferably 0 < R < 0.3, more preferably 0 < R < 0.25, more preferably 0 < R < 0.2, more preferably 0 < R < 0.15, more preferably 0 < R < 0.1, more preferably 0 < R < 0.05, more preferably 0 < R < 0.04.

[0045] According to an aspect, the present invention describes a process for preparing the inventive pigments, comprising the steps a) treating an alkaline vanadate solution with acid, phosphate ion solution and an acidic bismuth salt solution in a pH range of from 0.1 to 11 to form a precipitate; b) doping the precipitate with 1 or more materials selected from the group consisting of Mg, Ca, Al, P and combinations thereof; c) optional grinding step; d) coating the precipitate with 1 or more layers of metal phosphate selected from the group consisting of magnesium phosphate, aluminium phosphate, calcium phosphate and combinations thereof; e) optional further grinding step; f) calcining the precipitate at a temperature of > 300°C; and g) grinding the calcined product to form pigment particles.

[0046] In particular, the present invention especially preferably relates to a process for preparing a bismuth vanadate pigment, preferably a bismuth vanadate pigment as described above and in any one of embodiments 1 to 14 described hereinunder, the process comprising

[0047] (i) preparing a pigment core doped with one or more of phosphorus, magnesium, calcium, and aluminium, comprising

[0048] (1.1) preparing a bismuth vanadate pigment core precursor, comprising preparing an aqueous mixture from one or more of a bismuth reactant, a vanadate reactant and optionally a phosphorous dopant reactant, and precipitating said pigment core precursor from said aqueous mixture, obtaining an aqueous suspension comprising the pigment core precursor;

[0049] (1.2) adding one or more of a calcium dopant reactant, a magnesium dopant reactant, an aluminium dopant reactant and optionally a phosphorous dopant reactant to the aqueous suspension obtained according to (i.l), obtaining an aqueous mixture, and precipitating the pigment core doped with one or more of calcium, magnesium, aluminium and phosphorus from said aqueous mixture, obtaining an aqueous suspension comprising the doped pigment core;

[0050] (1.3) separating the doped pigment core from the aqueous suspension obtained according to (i.2); wherein in at least one of (i.l) and (i.2), a phosphorous dopant reactant is preferably employed; (ii) coating the doped pigment core obtained according to (i.3), comprising

[0051] (11.1) preparing an aqueous mixture comprising the doped pigment core obtained according to (i.3), one or more of a phosphorous coating reactant, an aluminium coating reactant, a calcium coating reactant and a magnesium coating reactant under coating conditions, obtaining an aqueous suspension comprising the doped pigment core coated with an oxidic coating precursor comprising one or more of magnesium, calcium, aluminium and phosphorous;

[0052] (11.2) separating the doped pigment core coated with the oxidic coating precursor from the suspension prepared according to (ii.l);

[0053] (iii) subjecting the doped pigment core coated with the oxidic coating precursor obtained according to (ii.2) to heat-treatment, obtaining the bismuth vanadate pigment, the pigment comprising a bismuth- and vanadium-containing core doped with one or more of magnesium, calcium, aluminium and phosphorus, the doped core being coated with an oxidic coating comprising one or more of magnesium, calcium, aluminium and phosphorous.

[0054] Further in particular, the present invention especially preferably relates to a process for preparing a bismuth vanadate pigment, preferably a bismuth vanadate pigment as described above and according to any one of embodiments 2 to 13 as described hereinunder, the process comprising

[0055] (i) preparing a pigment core doped with phosphorus, magnesium, calcium, and aluminium, comprising

[0056] (1.1) preparing a bismuth vanadate pigment core precursor, comprising preparing an aqueous mixture from a bismuth reactant, a vanadate reactant and optionally a phosphorous dopant reactant, and precipitating said pigment core precursor from said aqueous mixture, obtaining an aqueous suspension comprising the pigment core precursor;

[0057] (1.2) adding a calcium dopant reactant, a magnesium dopant reactant, an aluminium dopant reactant and optionally a phosphorous dopant reactant to the aqueous suspension obtained according to (i.l), obtaining an aqueous mixture, and precipitating the pigment core doped with one or more of calcium, magnesium, aluminium and phosphorus from said aqueous mixture, obtaining an aqueous suspension comprising the doped pigment core;

[0058] (1.3) separating the doped pigment core from the aqueous suspension obtained according to (i.2); wherein in at least one of (i.l) and (i.2), a phosphorous dopant reactant is employed;

[0059] (ii) coating the doped pigment core obtained according to (i.3), comprising

[0060] (ii.l) preparing an aqueous mixture comprising the doped pigment core obtained according to (i.3), a phosphorous coating reactant, an aluminium coating reactant, a calcium coating reactant and a magnesium coating reactant under coating conditions, obtaining an aqueous suspension comprising the doped pigment core coated with an oxidic coating precursor comprising magnesium, calcium, aluminium and phosphorous;

[0061] (ii.2) separating the doped pigment core coated with the oxidic coating precursor from the suspension prepared according to (ii.1);

[0062] (iii) subjecting the doped pigment core coated with the oxidic coating precursor obtained according to (ii.2) to heat-treatment, obtaining the bismuth vanadate pigment, the pigment comprising a bismuth- and vanadium-containing core doped with magnesium, calcium, aluminium and phosphorus, the doped core being coated with an oxidic coating comprising of magnesium, calcium, aluminium and phosphorous.

[0063] Step (i)

[0064] Step (i.l)

[0065] Preferably, the bismuth reactant according to (i.l) comprises bismuth in oxidation state III, more preferably one or more Bi(III) salts, more preferably one or more of Bi(III) acetate and BI(III) nitrate, wherein more preferably, the bismuth reactant according to (i.1) comprises, more preferably consists of Bi(III) nitrate. Preferably, the bismuth reactant according to (i.l) is employed as one or more aqueous solutions, more preferably one or more acidic aqueous solutions.

[0066] Preferably, the vanadate reactant according to (i.l) comprises one or more of ammonium metavanadate, ammonium orthovanadate, ammonium polyvanadate, at least one alkali metal metavanadates, at least one alkali metal orthovanadates, and at least one alkali metal polyvanadates, more preferably one or more of at least one alkali metal metavanadates, at least one alkali metal orthovanadates, and at least one alkali metal polyvanadates, more preferably one or more alkali metal metavanadates, more preferably one or more of potassium metavanadate and sodium metavanadate. Preferably, the vanadate reactant according to (i.l) is employed as one or more aqueous solutions.

[0067] According to (i.1), the bismuth reactant and the vanadate reactant are preferably employed at a V : Bi elemental ratio in the range of from 0.7:1 to 1.3:1, preferably in the range of from 0.8:1 to 1.2:1, more preferably in the range of from 0.9:1 to 1.1:1.

[0068] According to the present invention, it is preferred that preparing a bismuth vanadate pigment core precursor according to (i.l) comprises preparing an aqueous mixture from a bismuth reactant, a vanadate reactant and a phosphorous dopant reactant, and precipitating said pigment core precursor from said aqueous mixture, obtaining an aqueous suspension comprising the pigment core precursor.

[0069] In this context, it is preferred that the phosphorous dopant reactant according to (i.l) comprises one or more of phosphate ions and hydrogen phosphate ions. More preferably, the phosphorous dopant reactant according to (i.l) comprises one or more of phosphoric acid, at least one alkali metal phosphate and ammonium phosphate, more preferably one or more of phosphoric acid and at least one of sodium phosphate and ammonium phosphate. More preferably, the phosphorous dopant reactant according to (i.l) comprises, more preferably consists of phosphoric acid. Preferably, the phosphorous dopant reactant according to (i.l) is preferably employed as one or more aqueous solutions.

[0070] According to (i.l), the bismuth reactant, the vanadate reactant and the phosphorous dopant reactant are preferably employed at a P : (Bi+V) elemental ratio in the range of from 0.05:1 to 0.1:1, more preferably in the range of from 0.55:1 to 0.09:1, more preferably in the range of from 0.06:1 to 0.08:1.

[0071] Further, preparing a bismuth vanadate pigment core precursor according to (i.l) is preferably carried out at a temperature of the aqueous mixture according to (i.l) of at most 20 °C, more preferably at most 15 °C, more preferably at most 10 °C, more preferably less than 10 °C, in each case at ambient pressure.

[0072] Yet further, preparing a bismuth vanadate pigment core precursor according to (i.l) is preferably carried out at a pH of the aqueous mixture according to (i.l) in the range of from -1 to 11, more preferably in the range of from 0 to 10. Preferably, at the beginning of step (i.l), the pH of the aqueous mixture is in the range of from 9 to 11, more preferably in the range of from 9 to 10, and at the end of step (i.l), the pH of the aqueous mixture is preferably in the range of from - 1 to 2, more preferably in the range of from 0 to 1.

[0073] The pH of the aqueous mixture according to (i.l) in the range of from 9 to 11, preferably from 9 to 10, is preferably adjusted to said values using at least one base, preferably comprising one or more of ammonium hydroxide and at least one alkali metal hydroxide, wherein more preferably, the at least one base comprises, more preferably consists of sodium hydroxide.

[0074] Preferably, wherein during (i.l), at least one acid is added to the aqueous mixture, preferably to the aqueous mixture exhibiting a pH in the range of from 9 to 11, preferably from 9 to 10, wherein the at least one acid is preferably one or more of sulphuric acid and nitric acid, wherein more preferably, the at least one acid comprises, more preferably consists of nitric acid. Step (i.2)

[0075] With regard to step (i.2), it is preferred that the calcium dopant reactant comprises at least one calcium salt, more preferably one or more of calcium nitrate, calcium sulphate, calcium chloride, calcium carbonate, calcium hydroxide, and calcium acetate. More, the calcium dopant reactant according to (i.2) comprises, more preferably consists of calcium hydroxide.

[0076] As to the magnesium dopant reactant according to (i.2), it is preferred that it comprises at least one magnesium salt, more preferably one or more of magnesium nitrate, magnesium sulphate, magnesium chloride, magnesium carbonate, magnesium hydroxide, and magnesium acetate. More preferably, the magnesium dopant reactant according to (i.2) comprises, more preferably consists of magnesium hydroxide.

[0077] Regarding the aluminium dopant reactant according to (i.2), it is preferred that it comprises at least one aluminium containing salt, more preferably one or more of aluminium nitrate, aluminium sulphate, aluminium carbonate, aluminium hydroxide, aluminium acetate, sodium aluminate, and potassium aluminate. More preferably, the aluminium dopant reactant according to (i.2) comprises, more preferably consists of aluminium nitrate.

[0078] With regard to the phosphorous dopant reactant according to (i.2), it is preferred that it comprises one or more of phosphate ions and hydrogen phosphate ions, wherein more preferably, the phosphorous dopant reactant according to (i.2comprises one or more of phosphoric acid, at least one alkali metal phosphate and ammonium phosphate, more preferably comprising one or more of phosphoric acid and at least one of sodium phosphate and ammonium phosphate. More preferably, the phosphorous dopant reactant according to (i.2) comprises, more preferably consists of phosphoric acid.

[0079] According to the present invention, it is preferred that according to (i.2), two or more, more preferably three or more of a calcium dopant reactant, a magnesium dopant reactant, an aluminium dopant reactant and optionally a phosphorous dopant reactant are added to the aqueous suspension obtained according to (i.l), wherein more preferably, a calcium dopant reactant, a magnesium dopant reactant, and an aluminium dopant reactant are added to the aqueous suspension obtained according to (i.l).

[0080] Further according to (i.2), the aluminium dopant reactant is preferably employed at a Al : (Bi+V) elemental ratio in the range of from 0.003: 1 to 0.015: 1, more preferably in the range of from 0.006:1 to 0.012:1, more preferably in the range of from 0.008:1 to 0.010:1. Yet further according to (i.2), the calcium dopant reactant is preferably employed at a Ca : (Bi+V) elemental ratio in the range of from 0.005:1 to 0.050:1, more preferably in the range of from 0.010:1 to 0.030:1, more preferably in the range of from 0.015:1 to 0.025:1.

[0081] Still further according to (i.2), the magnesium dopant reactant is preferably employed at a Mg : (Bi+V) elemental ratio in the range of from 0.001:1 to 0.03:1, preferably in the range of from 0.002:1 to 0.02:1, more preferably in the range of from 0.005:1 to 0.015:1.

[0082] According to (i.2), precipitating the pigment core doped with one or more of calcium, magnesium, aluminium and phosphorus preferably comprises heating the aqueous mixture to a temperature of at least 80 °C, more preferably at least 85 °C, more preferably at least 90 °C, more preferably at least 95 °C, in each case at ambient pressure.

[0083] Further, for precipitating the pigment core doped with one or more of calcium, magnesium, aluminium and phosphorus according to (i.2), the pH of the aqueous mixture according to (i.2) is preferably adjusted to a value in the range of from 3 to 6, more preferably from 3.5 to 5.5, more preferably from 4 to 5. According to (i.2), the pH of the aqueous mixture is preferably adjusted to said values using at least one base, said base preferably comprising one or more of an alkali carbonate, an alkali hydrogen carbonate, an alkali hydroxide, and ammonia, more preferably comprising one or more of an alkali carbonate, wherein more preferably, the at least one base comprises, more preferably consists of sodium carbonate. Preferably, in case the pH should decrease during (i.2), the at least one base is used keep the pH essentially constant during. For carrying out (i.2), it is preferred that the mixture subjected to said precipitation conditions is agitated, preferably mechanically agitated, more preferably stirred. The reaction time for the precipitation as described may vary according to the respective batch size. Typical reaction times are in the range of from 2 to 360 min or from 5 to 240 min or from 10 to 140 min.

[0084] Step (i.3)

[0085] According to step (i.3), it is preferred that separating the doped pigment core from the aqueous suspension comprises

[0086] (i.3.1) subjecting the aqueous suspension obtained according to (i.2), preferably after cooling to a temperature in the range of from 10 to 50 °C, preferably from 15 to 40 °C, more preferably from 20 to 30 °C, to solid-liquid separation, preferably to one or more of filtration and centrifugation, more preferably to filtration.

[0087] Further preferably, after (i.3.1), the process according to (i.3) comprises (1.3.2) subjecting the doped pigment core separated by solid-liquid separation according to

[0088] (1.3.1) to washing, preferably to washing with an aqueous medium, preferably water.

[0089] According to the present, the washing according to (i.3.2) is preferably carried out until the obtained washing water is salt-free. The term “salt-free” as used in this context of the present invention refers to a conductivity of the washing water of at most 500 p.S / cm.

[0090] Yet further preferably, according to (i.3), separating the doped pigment core from the aqueous suspension further comprises after (i.3.1) or after (i.3.2), preferably after (i.3.2)

[0091] (1.3.3) subjecting the doped pigment core separated by solid-liquid separation according to

[0092] (1.3.1), preferably the washed doped pigment core according to (i.3.2), to grinding, preferably to wet-milling.

[0093] According to (i.3.3), the preferred wet-milling allows for omitting a preceding drying stage.

[0094] For grinding according to (i.3.3), a mixer, a ball mill, a bead mill, a rotor-stator disperser, a 3- rolls mill, an impeller mill, a shaking machine, a pen mill, impact mill or a jet mill can be used.

[0095] Preferably, the particle size of the ground doped pigment core respectively obtained is in the range of from 0.1 to 2 pm, more preferably from 0.2 to 1.8 pm, more preferably from 0.3 to 1.6 pm.

[0096] To improve the precipitation quality, especially to increase the color strength and the chroma value C* of the final pigment product, it is generally conceivable to introduce additional processing steps, such as for example, high-speed stirring; conducting the precipitation inside a bead mill; using rotor stator high shear equipment during precipitation; adding a Bi and V containing pigment at the beginning of the precipitation which can be an intermediate or finalized product containing the aforementioned elements; adding soluble or insoluble salts of alkaline halogenides or alkaline sulphates like NaCl or Na2SO4; or adding an alkaline pyrophosphate as a dispersing agent. According to an aspect of the present invention, such additional process steps are not carried out.

[0097] Step (ii)

[0098] According to step (ii) of the process of the present invention, the doped core obtained from (i.3) is suitably coated with an oxidic coating. In this context, it is generally conceivable that materials for metal phosphate coatings are the phosphates, especially the orthophosphates of alkaline earth metals, especially magnesium and calcium and of aluminium, which may also be present mixed in a single layer. Depending on the particle size and the specific surface area of the bismuth vanadate used, the stabilized bismuth vanadate pigments of the present application generally may contain from 1 to 40 mol-%, preferably from 2 to 20 mol-% of coating material, based on the coated pigment. To prepare the bismuth vanadate pigments of the present application, the coatings are advantageously precipitated wet-chemically onto the selected base pigment. To deposit a metal phosphate layer, a slurry of the substrate (which can be an uncoated bismuth vanadate pigment, or a bismuth vanadate pigment already coated with metal phosphates), a solution of a calcium, magnesium and / or aluminium salt and phosphoric acid or other soluble phosphate sources may be thoroughly mixed, preference being given to the use of aqueous solutions and slurries. Process-wise it is possible to proceed in various ways: the substrate slurry can be introduced as an initial charge and the calcium, magnesium and / or aluminium salt solution and the phosphoric acid or a different phosphate ion solution added at the same time. However, it is also possible to add the solutions of calcium, magnesium and / or aluminium and phosphoric acid or a different phosphate ion solution sequentially. Further, it is possible to introduce the calcium, magnesium and / or aluminium salt solutions as an initial charge and to add the phosphoric acid or a different phosphate ion solution together with the substrate slurry. Further, it is possible to introduce the phosphoric acid or other soluble phosphate sources as an initial charge and add the substrate slurry together with a calcium, magnesium and / or aluminium salt solution. The salt solutions are preferably used in amounts which substantially correspond to the desired stoichiometry to obtain the desired molar ratios of the metal phosphates. Phosphoric acid may generally be used in excess.

[0099] An especially preferred process step (ii) is described in the following.

[0100] Step (ii.l)

[0101] Preferably, the phosphorous coating reactant comprises one or more of phosphate ions and hydrogen phosphate ions. More preferably, the phosphorous coating reagent according to (ii.l) comprises one or more of phosphoric acid, at least one alkali metal phosphate and ammonium phosphate, more preferably one or more of phosphoric acid and at least one of sodium phosphate and ammonium phosphate, wherein more preferably, the phosphorous coating reactant according to (ii.l) comprises, more preferably consists of phosphoric acid

[0102] Further preferably, the aluminium coating reactant according to (ii.l) comprises at least one aluminium containing salt, more preferably one or more of aluminium nitrate, aluminium sulphate, aluminium carbonate, aluminium hydroxide, aluminium acetate, sodium aluminate, and potassium aluminate. More preferably, the aluminium coating reactant according to (ii.l) comprises, more preferably consists of aluminium sulphate. Yet further preferably, the calcium coating reactant according to (ii.l) comprises at least one calcium salt, more preferably one or more of calcium nitrate, calcium sulphate, calcium chloride, calcium carbonate, calcium hydroxide, and calcium acetate. More preferably, the calcium coating reactant according to (ii.l) comprises, more preferably consists of calcium nitrate.

[0103] Still further preferably, the magnesium coating reactant according to (ii.l) comprises at least one magnesium salt, more preferably one or more of magnesium nitrate, magnesium sulphate, magnesium chloride, magnesium carbonate, magnesium hydroxide, and magnesium acetate. More preferably, the magnesium coating reactant according to (ii.1) comprises, more preferably consists of magnesium nitrate.

[0104] Preferably according to (ii.l) , the process comprises preparing an aqueous mixture comprising the doped pigment core obtained according to (i.3), a phosphorous coating reactant and two or more of an aluminium coating reactant, a calcium coating reactant and a magnesium coating reactant under coating conditions, wherein more preferably, (ii.l) comprises preparing an aqueous mixture comprising the doped pigment core obtained according to (i.3), a phosphorous coating reactant, an aluminium coating reactant, a calcium coating reactant and a magnesium coating reactant under coating conditions.

[0105] Said coating conditions according to (ii.l) preferably comprise a temperature of the aqueous mixture according to (ii.l) in the range of from 4o to 90 °C, more preferably from 50 to 90 °C, more preferably 60 to 90 °C, preferably from 70 to 85 °C, more preferably from 75 to 85 °C, in each case at ambient pressure.

[0106] Further, said coating conditions according to (ii.l) comprise a pH of the aqueous mixture according to (ii.1) in the range of from 4.5 to 7.5, preferably from 5 to 7, more preferably from 5.5 to 7, more preferably from 6 to 6.5.

[0107] The pH of the aqueous mixture is adjusted to said values preferably using at least one base, said base at least one preferably comprising one or more of ammonium hydroxide, at least one alkali metal carbonate, at least one alkali metal hydrogen carbonate and at least one alkali metal hydroxide, wherein more preferably, the at least one base comprises, more preferably consists of one or more of potassium hydroxide and sodium hydroxide. More preferably, the at least one base comprises, more preferably consists of sodium hydroxide. Preferably, the at least one base is employed as at least one aqueous solution. Such aqueous solutions may exhibit 5 to 50 % strength by weight, for example in case of potassium hydroxide and sodium hydroxide; or 5 to 30 % strength by weight, for example in case of alkali metal carbonate. Should it be necessary to use an acid in order to adjust the pH, a suitable acid comprises, for example nitric acid, for example with 65 % strength by weight.

[0108] According to a preferred process step (ii.l), the aqueous mixture is prepared by adding two or more of the aluminium coating reactant, the calcium coating reactant and the magnesium coating in subsequent steps. Preferably, (ii.l) comprises

[0109] (ii.1.1 ) preparing a first aqueous mixture comprising a first coating reactant;

[0110] (ii.1.2) adding a second coating reactant to the first aqueous mixture, obtaining a second aqueous mixture;

[0111] (ii.1.3) optionally or preferably adding a third coating reactant to the first aqueous mixture, obtaining a third aqueous mixture; wherein in at least one of steps (ii.1.1), (ii.1.2) and (ii.l.3), preferably in at least two of steps

[0112] (11.1.1), (ii.1.2) and (ii.l.3), more preferably in at least steps (ii.1.2) and (ii.1.3), a phosphorous coating reactant is added.

[0113] Preferably, the pH of the first aqueous mixture according to (ii.1.1) is adjusted to a value in the range of from 5 to 7, more preferably from 5.5 to 7, more preferably from 6 to 6.5, said adjusting comprising adding at least one base, said base at least one preferably comprising one or more of ammonium hydroxide, at least one alkali metal carbonate, at least one alkali metal hydrogen carbonate and at least one alkali metal hydroxide, wherein more preferably, the at least one base comprises, more preferably consists of one or more of potassium hydroxide and sodium hydroxide. More preferably, the at least one base comprises, more preferably consists of sodium hydroxide., preferably comprising one or more of ammonium hydroxide and at least one alkali metal hydroxide, wherein more preferably, the at least one base comprises, more preferably consists of sodium hydroxide.

[0114] More preferably, (ii.l) comprises

[0115] (ii.1.1 ) preparing a first aqueous mixture comprising a first coating reactant;

[0116] (11.1.2) adding a second coating reactant to the first aqueous mixture, obtaining a second aqueous mixture;

[0117] (ii.1.3) adding a third coating reactant to the first aqueous mixture, obtaining a third aqueous mixture; wherein in at least one of steps (ii.1.1), (ii.1.2) and (ii.l.3), preferably in at least two of steps (ii.1.1), (ii.1.2) and (ii.l.3), more preferably in at least steps (ii.1.2) and (ii.l.3), at least one phosphate source is added.

[0118] Preferably, the first coating reactant according to (ii.1.1) comprises, preferably consists of the aluminium coating reactant, the second coating reactant according to (ii.1.2) comprises, preferably consists of the calcium coating reactant, and the third coating reactant according to (ii.1.3) comprises, preferably consists of the magnesium coating reactant.

[0119] According to (ii.l), the aluminium coating reactant is preferably employed at a Al : (Bi+V) elemental ratio in the range of from 0.002:1 to 0.1:1, more preferably in the range of from 0.005:1 to 0.09:1, more preferably in the range of from 0.009:1 to 0.08:1, wherein (Bi+V) refers to the amount of Bi and V comprised in the doped pigment core employed in (ii.1).

[0120] Further according to (ii.1), the calcium coating reactant is preferably employed at a Ca : (Bi+V) elemental ratio in the range of from 0.001:1 to 0.08:1, more preferably in the range of from 0.002: 1 to 0.07: 1 , more preferably in the range of from 0.005 : 1 to 0.06: 1 , wherein (Bi+V) refers to the amount of Bi and V comprised in the doped pigment core employed in (ii.l).

[0121] Yet further according to (ii.l), the magnesium coating reactant is preferably employed at a Mg : (Bi+V) elemental ratio in the range of from 0.001:1 to 0.07:1, more preferably in the range of from 0.002: 1 to 0.06: 1 , more preferably in the range of from 0.004: 1 to 0.055: 1 , wherein (Bi+V) refers to the amount of Bi and V comprised in the doped pigment core employed in (ii.l).

[0122] Still further according to (ii.l), the the phosphorous coating reactant is preferably employed at a P : (Bi+V) elemental ratio in the range of from 0.002:1 to 0.2:1, more preferably in the range of from 0.005:1 to 0.19:1, more preferably in the range of from 0.01:1 to 0.18:1, wherein (Bi+V) refers to the amount of Bi and V comprised in the doped pigment core employed in (ii.l).

[0123] According to the present invention, in particular described in the example section herein, it was surprisingly found that while the presence of the oxidic coating is necessary for achieving the desired properties of the pigment, there is a clear tendency that the lower the amount of the one or more, preferably two or more, more preferably three or more, more preferably all of Al, Ca, Mg and P used for preparing the oxidic coating according to step (ii), the higher the (improved) color strength of the pigment. In particular, for the elemental ratio R of the one or more, preferably two or more, more preferably three or more, more preferably all of Al, Ca, Mg and P used for preparing the oxidic coating according to step (ii), relative to the amount of Bi and V, (Bi+V), comprised in the doped core, it is preferred that 0 < R < 0.4, more preferably 0 < R < 0.35, more preferably 0 < R < 0.3, more preferably 0 < R < 0.25, more preferably 0 < R < 0.2, more preferably 0 < R < 0.15, more preferably 0 < R < 0.1, more preferably 0 < R < 0.05, more preferably 0 < R < 0.04.

[0124] Step (ii.2)

[0125] Further according to stage (ii) of the process of the present invention, the coated doped pigment core is separated from the aqueous suspension according to (ii.2).

[0126] In this context, it is preferred according to (ii.2) that separating the doped pigment core coated with the oxidic coating precursor from the aqueous suspension comprises

[0127] (11.2.1) subjecting the aqueous suspension obtained according to (ii.l), preferably after cooling to a temperature in the range of from 10 to 50 °C, preferably from 15 to 40 °C, more preferably from 20 to 30 °C, to solid-liquid separation, preferably to one or more of filtration and centrifugation, more preferably to filtration.

[0128] Preferably, separating the doped pigment core coated with the oxidic coating precursor from the aqueous suspension according to (ii.2) further comprises, after (ii.2.1),

[0129] (11.2.2) subjecting the doped pigment core coated with the oxidic coating precursor separated by solid- liquid separation according to (ii.2.1) to washing, preferably to washing with an aqueous medium, preferably water.

[0130] According to the present, the washing according to (ii.2.2) is preferably carried out until the obtained washing water is salt-free. The term “salt-free” as used in this context of the present invention refers to a conductivity of the washing water of at most 500 pS / cm.

[0131] Further preferably, separating the doped pigment core coated with the oxidic coating precursor from the aqueous suspension further comprises after (ii.2.1) or after (ii.2.2), preferably after

[0132] (11.2.2)

[0133] (11.2.3) subjecting the doped pigment core coated with the oxidic coating precursor separated by solid-liquid separation according to (ii.2.1), preferably the washed doped pigment core coated with the oxidic coating precursor according to (ii.2.2), to grinding, preferably to wet-milling;

[0134] (11.2.4) optionally or preferably subjecting the ground doped pigment core coated with the oxidic coating precursor to deagglomeration.

[0135] Preferably, the particle size of the obtained doped pigment core coated with the oxidic coating precursor is in the range of from 0.1 to 2 pm, more preferably from 0.2 to 1.8 pm, more preferably from 0.3 to 1.6 pm.

[0136] Step (iii)

[0137] Preferably, the coated doped pigment core obtained according to stage (ii) of the process of the present invention is further subjecting to a subsequent heat-treatment stage (iii). This heat treatment stage preferably comprises (111.1) subjecting the doped pigment core coated with the oxidic coating precursor obtained according to (ii.3) to drying, preferably at a temperature in the range of from 90 to 175 °C, more preferably from 105 to 150 °C, more preferably from 110 to 130 °C, in each case at ambient pressure;

[0138] (111.2) subjecting the dried doped pigment core coated with the oxidic coating precursor obtained according to (iii.l) to calcination, preferably at a temperature in the range of from 450 to 650 °C, more preferably from 500 to 600 °C, more preferably from 525 to 575 °C, in each case at ambient pressure, obtaining the bismuth vanadate pigment comprising a bismuth- and vanadium-containing core doped with one or more of magnesium, calcium, aluminium and phosphorus, the doped core being coated with an oxidic coating comprising one or more of magnesium, calcium, aluminium and phosphorous.

[0139] The drying according to (iii.l) may also comprise spray-drying. The calcination time according to (iii.2) is usually dependent of the batch size; typical calcination times are in the range of from 0.5 to 4 h. The calcination can be performed under any atmosphere, preferably under inert gas atmosphere such as a nitrogen atmosphere or an oxidizing atmosphere such as air.

[0140] After calcination, the bismuth vanadate pigment is preferably gradually or continuously cooled, preferably to a temperature in the range of from 10 to 50 °C, more preferably from 15 to 40 °C, more preferably from 20 to 30 °C. Usually, the cooling time depends on the batch size. Typical cooling times are in the range of from 1 to 10 h.

[0141] Steps (iv) to (vii)

[0142] Optionally, the bismuth vanadate pigment obtained according to stage (iii) of the process of the present invention is further subjecting to a subsequent grinding stage (iv). This grinding stage preferably comprises

[0143] (iv) subjecting the bismuth vanadate pigment obtained according to (iii) to grinding, preferably to one or more of wet-milling and dry-milling.

[0144] For grinding according to (iv), a mixer, a ball mill, a bead mill, a rotor-stator disperser, a 3-rolls mill, an impeller mill, a shaking machine, a pen mill, impact mill or a jet mill can be used.

[0145] Preferably, the particle size of the obtained bismuth vanadate pigment is in the range of from 0.1 to 2 pm, more preferably from 0.2 to 1.8 pm, more preferably from 0.3 to 1.6 pm.

[0146] In particular in case that stage (iv) comprises subjecting the bismuth vanadate pigment obtained according to (iii) to dry- milling, the process preferably further comprising after (iv) (v) suspending the dry-milled bismuth vanadate pigment in water, and subjecting the obtained aqueous suspension to agitation, preferably mechanical agitation, more preferably stirring;

[0147] (vi) subjecting the stirred aqueous suspension obtained from (v) to drying, preferably at a temperature in the range of from 100 to 175 °C, more preferably from 105 to 150 °C, more preferably from 110 to 130 °C, in each case at ambient pressure, obtaining the dried bismuth vanadate pigment;

[0148] (vii) optionally or preferably subjecting the dried bismuth vanadate pigment to deagglomeration .

[0149] The present invention further relates to bismuth vanadate pigment comprising a bismuth- and vanadium-containing core doped with one or more of magnesium, calcium, aluminium and phosphorus, the doped core being coated with an oxidic coating comprising one or more of magnesium, calcium, aluminium and phosphorous, obtainable or obtained by a process as described above and / or according a process according to any one of embodiments 15 to 62 as disclosed herein. In particular, the present invention further relates to a bismuth- and vanadium- containing pigment, obtainable or obtained by a process as described above and / or according a process according to any one of embodiments 15 to 62 as disclosed herein, wherein the respectively obtained pigment exhibits the features as defined above and in particular the features according to any one of embodiments 2 to 15 as disclosed herein.

[0150] Further, the present invention relates to a composition, comprising the pigment as described hereinabove and / or a pigment according to any one of embodiments 1 to 15 and / or 63 to 76 as disclosed herein, said composition preferably being selected from the group consisting of coating compositions, paints, printing inks, liquid inks, plastics, films, fibers, glazes, and automotive paints.

[0151] Preferably, the pigments of the present application may be used in various materials, for example high molecular weight materials, especially high molecular weight organic material. Preferred fields of use of the pigments are as colorants for paints, printing inks, liquid inks, plastics, rubber, fibres, and films. Paints are aqueous or solvent-bome coating materials and also powder coating materials, in which the pigments of the present application may be employed alone or in combination with extenders, white pigments, chromatic pigments or black pigments. Binders that may be used are not limited and include those found in the general inks and coatings sector. Examples of coating materials which may be colored with the pigments of the present application include: oil-based materials (based on linseed oil or polyurethane oils) cellulose-based coating materials (NC, CAB, CAP) vinyl coating materials (based on PVC, PVDF, VC copolymer, polyvinyl acetate, polyvinyl ester dispersion, polyvinyl alcohol, polyvinyl acetal, polyvinyl ether, polystyrene, styrene copolymers) acrylate coating materials alkyd coating materials saturated polyester coating materials polyurethane coating materials (one pack, two pack) epoxy coating materials silicone coating materials silicate coating materials (based on waterglass, alkyl silicates)

[0152] These coating systems are described in further detail in D. Stoye, W. Freitag, Paints, Coatings and Solvents, Second Edition, 1998, Wiley-VCH.

[0153] Combinations with effect pigments are also possible and lead to special effects. Effect pigments include platelet- shaped metallic and / or oxidic effect pigments, generally known in the art.

[0154] The pigments of the present application may also advantageously be used in color customary plastics and blends of plastics, either as pigments alone or in combination with white, chromatic, and black pigments, and in combination with all typical additives and stabilizers. Suitable plastics include unplasticized and plasticized PVC, polyolefins, and also all engineering plastics such as ABS, polystyrene, polyamide, polyester, polycarbonate, polyether ketone, and also polyurethanes and rubber systems. The pigments can be incorporated by means of typical mixing, blending, kneading and extrusion techniques.

[0155] The pigments may be used in any amount, typically from 0.01 to 75 weight-%, preferably from 0.01 to 50 weight-%, based on the total weight of the material to be colored.

[0156] Further, the present application relates to the use of the pigments as for coloring coating compositions, paints, printing inks, liquid inks, plastics, films, fibers, or glaze for ceramic or glass. The coating composition may be an automotive, decorative or industrial coating composition or paint. In one embodiment, the pigment is used as a colorant for an automotive, decorative, industrial coating composition, a paint or plastic.

[0157] Further, the present invention relates to a process for coloring a coating composition, a paint, a printing ink, a liquid ink, plastics, a film, a fibre, or a glaze for ceramics or glass is provided, which process comprises adding thereto a pigment as defined herein. Yet further, the present invention relates to a method for increasing the color strength of a pigment composition comprising a bismuth- and vanadium-containing core, said core being coated with an oxidic coating comprising one or more of magnesium, calcium, aluminium and phosphorous, the method comprising doping said core, prior to coating, with one or more of magnesium, calcium, aluminium and phosphorus. Further, the present invention also relates to the use of one or more of magnesium, calcium, aluminium and phosphorus as a bismuth- and vanadium-containing core doping agent for increasing the color strength of a pigment composition comprising said bismuth- and vanadium-containing core, the core being coated with an oxidic coating comprising one or more of magnesium, calcium, aluminium and phosphorous. Preferably according to this method and / or use, two or more of magnesium, calcium, aluminium and phosphorus, more preferably three or more of magnesium, calcium, aluminium and phosphorus, more preferably magnesium, calcium, aluminium and phosphorus are employed as core doping agent. Further preferably according to this method and / or use, the core is coated with an oxidic coating comprising two or more of magnesium, calcium, aluminium and phosphorous, more preferably two or more of magnesium, calcium, aluminium and phosphorous, more preferably magnesium, calcium, aluminium and phosphorous. Preferably according to this method and / or use, the color strength is increased by at least 5 %, preferably at least 10 %, more preferably at least 15 %, more preferably at least 20 %, more preferably at least 25 %, more preferably at least 30 %, in each case based on the color strength of the non-doped pigment composition. Further preferably according to this method and / or use, the pigment composition exhibiting the non-increased color strength exhibits one or more, more preferably two or more, more preferably all of the following features: a hue angle h° of at least 90, preferably in the range of from 90 to 95, more preferably from 91 to 95, more preferably from 91 to 94, the hue angle h° being determined as described in Reference Example 2; a chroma value C* of at least 90, preferably at least 91, more preferably at least 92, more preferably in the range of from 92 to 97, more preferably in the range of from 92 to 96, the chroma value C* being determined as described in Reference Example 2; a lightness value L* of at least 80, preferably at least 81 , more preferably at least 82, more preferably in the range of from 82 to 87, more preferably from 82 to 86, the lightness value L* being determined as described in Reference Example 2.

[0158] Still further, the present invention relates to a method for increasing the color strength of a pigment composition comprising a bismuth- and vanadium-containing core, said core being doped with one or more of magnesium, calcium, aluminium and phosphorus, the method comprising coating the doped core with an oxidic coating comprising one or more of magnesium, calcium, aluminium and phosphorous. Further, the present invention relates to the use of an oxidic coating comprising one or more of magnesium, calcium, aluminium and phosphorous as doped core coating for increasing the color strength of a pigment composition comprising a bismuth- and vanadium-containing core, said core being doped with one or more of magnesium, calcium, aluminium and phosphorus. Preferably according to this method and / or use, the oxidic coating comprises two or more of magnesium, calcium, aluminium and phosphorous, more preferably three or more of magnesium, calcium, aluminium and phosphorous, more preferably magnesium, calcium, aluminium and phosphorous. Further preferably according to this method and / or use, the core is doped with two or more of magnesium, calcium, aluminium and phosphorus, more preferably with three or more of magnesium, calcium, aluminium and phosphorus, more preferably with magnesium, calcium, aluminium and phosphorus. Preferably according to this method and / or use, the color strength is increased by at least 2 %, preferably at least 3 %, more preferably at least 4 %, more preferably at least 5 %, more preferably at least 6 %, more preferably at least 7 %, in each case based on the color strength of the non-coated pigment composition. Further preferably according to this method and / or use, the pigment composition exhibiting the non-increased color strength exhibits one or more, more preferably two or more, more preferably all of the following features: a hue angle h° of at least 90, preferably in the range of from 90 to 95, more preferably from 91 to 95, more preferably from 91 to 94, the hue angle h° being determined as described in Reference Example 2; a chroma value C* of at least 90, preferably at least 91, more preferably at least 92, more preferably in the range of from 92 to 97, more preferably in the range of from 92 to 96, the chroma value C* being determined as described in Reference Example 2; a lightness value L* of at least 80, preferably at least 81 , more preferably at least 82, more preferably in the range of from 82 to 87, more preferably from 82 to 86, the lightness value L* being determined as described in Reference Example 2.

[0159] As to the above-described methods and / or uses, it is preferred that the pigment composition exhibiting the increased color strength is prepared according to a process as described hereinabove and according to any one of embodiments 15 to 62 as disclosed herein. Further preferably according to these methods and / or uses, the pigment composition exhibiting the increased color strength exhibits the features as defined hereinabove and in any one of embodiments 5 to 14 as disclosed herein.

[0160] The following set of paragraphs and combinations of paragraphs resulting from the dependencies and back-references as indicated describe a conceivable aspect of the present invention. It is noted that in each instance where a range of paragraphs is mentioned, for example in the context of a term such as "The pigment of any one of paragraphs 1 to 5", every paragraphs in this range is meant to be explicitly disclosed for the skilled person, i.e. the wording of this term is to be understood by the skilled person as being synonymous to "The pigment of any one of paragraphs 1, 2, 3, 4 and 5". Further, it is explicitly noted that the following set of paragraphs is not the set of claims determining the extent of protection, but represents a suitably structured part of the description directed to general and specific aspects of the present invention:

[0161] 1. A bismuth vanadate pigment comprising a bismuth and vanadium-containing core doped with 1 or more dopants and coated with 1 or more metal phosphates.

[0162] 2. The pigment of paragraph 1, wherein the dopants comprise 1 or more, preferably 2 or more, more preferably 3 or more, more preferably all 4 dopants selected from the group consisting of Mg, Ca, Al and P.

[0163] 3. The pigment of paragraph 1 or 2, wherein metal phosphates comprise 1 or more, preferably 2 or more, more preferably all 3 selected from the group consisting of magnesium phosphate, aluminium phosphate, and calcium phosphate.

[0164] 4. The pigment of any one of paragraphs 1 to 3, wherein the Bi, V, Mg, Al, Ca and P are present in molar ratios corresponding to Formula (I)

[0165] Bi Mga Alb CacVdPeOf (I) wherein

[0166] 0 < a < 0.20; preferably 0.001 < a < 0.20; more preferably 0.001 < a < 0.15; more preferably 0.005 < a < 0.10;

[0167] 0 < b < 0.20; preferably 0.001 < b < 0.20; more preferably 0.001 < b < 0.15; more preferably 0.005 < b < 0.10;

[0168] 0 < c < 0.32; preferably 0.001 < c < 0.30; more preferably 0.001 < c < 0.28; more preferably 0.005 < c < 0.26;

[0169] 0.50 < d < 2.0; preferably 0.65 < d < 1.8;

[0170] 0 < e < 0.8; preferably 0.001 < e < 0.7; more preferably 0.001 < e < 0.6, more preferably 0.01 < e < 0.5; wherein (a + b + c + e) > 0 and f denotes the number of oxygen atoms for satisfying the valence requirements of the cations.

[0171] 5. The pigment of any one of paragraphs 1 to 4, wherein the particle size is in the range of from 0.2 to 3.0 pm, preferably from 0.25 to 2 pm, more preferably from 0.3 to 1.4 pm.

[0172] 6. The pigment of any one of paragraphs 1 to 5, wherein the bismuth is selected from the group consisting of Bi(III) nitrate, Bi(III) acetate, and a combination thereof.

[0173] 7. The pigment of any one of paragraphs 1 to 6, wherein the vanadium is selected from the group consisting of ammonium, alkali metal meta-, ortho-, poly-, potassium and sodium metavanadate and combinations thereof.

[0174] 8. The pigment of any one of paragraphs 1 to 7, wherein the pigment is substantially free of Si and Mo.

[0175] 9. The pigment of any one of paragraphs 1 to 8, wherein the hue angle (h°) is in the range of from 90 to 95.

[0176] 10. The pigment of any one of paragraphs 1 to 9, wherein the chroma value C* is > 90. 11. The pigment of any one of paragraphs 1 to 10, wherein the lightness value L* is > 80.

[0177] 12. The pigment of any one of paragraphs 1 to 11, wherein the color strength is > 105, preferably > 107 vs. a comparative bismuth vanadate pigment not comprising both the dopants and metal phosphate coatings of the present application.

[0178] 13. A composition comprising the pigment of any one of paragraphs 1 to 12, the composition being selected from the group consisting of coating compositions, paints, printing inks, liquid inks, plastics, films, fibers, glazes, and automotive paints.

[0179] 14. A process for preparing a bismuth vanadate pigment, comprising the steps a) treating an alkaline vanadate solution with acid, phosphate ion solution and an acidic bismuth salt solution in a pH range of from 0.1 to 11 to form a precipitate; b) doping the precipitate with 1 or more materials selected from the group consisting of Mg, Ca, Al, P and combinations thereof; c) optional grinding step; d) coating the precipitate with 1 or more layers of metal phosphate selected from the group consisting of magnesium phosphate, aluminium phosphate, calcium phosphate and combinations thereof; e) optional further grinding step; f) calcining the precipitate at a temperature of > 300°C; and g) grinding the calcined product to form pigment particles.

[0180] 15. The process of paragraph 14, wherein the acid in step a) is nitric acid.

[0181] 16. The process of paragraph 14 or 15, wherein the metal phosphates are introduced in separate application layers, each layer comprising only one phosphate.

[0182] 17. The process of any one of paragraphs 14 to 16, wherein the Bi, V, Mg, Al, Ca and P are present in molar ratios corresponding to Formula (I)

[0183] Bi MgaAlb CacVdPeOf (I) wherein:

[0184] 0 < a < 0.20; preferably 0.001 < a < 0.20; more preferably 0.001 < a < 0.15; more preferably 0.005 < a < 0.10;

[0185] 0 < b < 0.20; preferably 0.001 < b < 0.20; more preferably 0.001 < b < 0.15; more preferably 0.005 < b < 0.10;

[0186] 0 < c < 0.32; preferably 0.001 < c < 0.30; more preferably 0.001 < c < 0.28; more preferably 0.005 < c < 0.26;

[0187] 0.50 < d < 2.0; preferably 0.65 < d < 1.8;

[0188] 0 < e < 0.8; preferably 0.001 < e < 0.7; more preferably 0.001 < e < 0.6, more preferably 0.01 < e < 0.5; wherein (a + b + c + e) > 0; and f denotes the number of oxygen atoms for satisfying the valence requirements of the cations. 18. The process of any one of paragraphs 14 to 17, comprising the additional steps of stirring the milled pigment in water, drying at 120 °C, and deagglomerating.

[0189] 19. The process of any one of paragraphs 14 to 18, comprising the additional steps of using a dry- milling grinding technique after the calcination step.

[0190] 20. The process of any one of paragraphs 14 to 19, wherein the resultant pigment exhibits a color strength > 105, more preferably > 107 vs. a comparative bismuth vanadate pigment not comprising both the dopants and metal phosphate coatings of the present application.

[0191] 21. A bismuth vanadate pigment, resulting from the process of any one of paragraphs 14 to 20.

[0192] 22. A bismuth vanadate pigment, obtainable or obtained by a process of any one of paragraphs 14 to 20.

[0193] In particular, the present invention is especially preferably illustrated by the following set of embodiments and combinations of embodiments resulting from the dependencies and back- references as indicated. In particular, it is noted that in each instance where a range of embodiments is mentioned, for example in the context of a term such as "The pigment of any one of embodiments 1 to 5", every paragraph in this range is meant to be explicitly disclosed for the skilled person, i.e. the wording of this term is to be understood by the skilled person as being synonymous to "The pigment of any one of embodiments 1, 2, 3, 4 and 5". Further, it is explicitly noted that the following set of embodiments is not the set of claims determining the extent of protection, but represents a suitably structured part of the description directed to general and specific aspects of the present invention.

[0194] 1. A bismuth vanadate pigment comprising a bismuth- and vanadium-containing core doped with one or more of magnesium, calcium, aluminium and phosphorus, the doped core being coated with an oxidic coating comprising one or more of magnesium, calcium, aluminium and phosphorous.

[0195] 2. The pigment of embodiment 1, wherein the oxidic coating comprises two or more of magnesium, calcium, aluminium and phosphorous, preferably three or more of magnesium, calcium, aluminium and phosphorous, more preferably magnesium, calcium, aluminium and phosphorous.

[0196] 3. The pigment of embodiment 1 or 2, wherein the oxidic coating comprises one or more of magnesium oxide, magnesium phosphate, calcium oxide, calcium phosphate, aluminium oxide and aluminium phosphate.

[0197] 4. The pigment of any one of embodiments 1 to 3, wherein the bismuth- and vanadium- containing core is doped with two or more of magnesium, calcium, aluminium and phosphorus, preferably with three or more of magnesium, calcium, aluminium and phosphorus, more preferably with magnesium, calcium, aluminium and phosphorus. The pigment of any one of embodiments 1 to 4, characterized by a composition according to formula (I)

[0198] Bi MgaAlbCacVdPeOf (I) wherein

[0199] 0.025 < a < 0.20; preferably 0.025 < a < 0.15; more preferably 0.025 < a < 0.10;

[0200] 0.025 < b < 0.20; preferably 0.025 < b < 0.15; more preferably 0.025 < b < 0.10;

[0201] 0.045 < c < 0.30; preferably 0.045 < c < 0.28; more preferably 0.045 < c < 0.26;

[0202] 0.50 < d < 2.0; preferably 0.60 < d < 1.9; more preferably 0.65 < d < 1.8; wherein e and f denote the number of phosphorous and oxygen atoms for satisfying the valence requirements of formula (I); wherein preferably 0.1 < e < 0.5; more preferably 0.13 < e < 0.45; more preferably 0.15 < e < 0.4. The pigment of any one of embodiments 1 to 5, characterized by a silicon content of at most 2000 weight-ppm, preferably at most 1500 weight-ppm, more preferably at most 1000 weight-ppm, calculated as elemental Si, wherein more preferably, the pigment is substantially free of silicon. The pigment of any one of embodiments 1 to 6, characterized by a molybdenum content of at most 1500 weight-ppm, preferably at most 1000 weight-ppm, more preferably at most 800 weight-ppm, calculated as elemental Mo, wherein more preferably, the pigment is substantially free of molybdenum. The pigment of any one of embodiments 1 to 7, characterized by a zinc content of at most 2000 weight-ppm, preferably at most 1500 weight-ppm, more preferably at most 1000 weight-ppm, calculated as elemental Zn, wherein more preferably, the pigment is substantially free of zinc. The pigment of any one of embodiments 1 to 8, being in particulate form, exhibiting a particle size in the range of from 0.2 to 3.0 pm, preferably from 0.25 to 2 pm, more preferably from 0.3 to 1.4 pm, the particle size being determined as described in Reference Example 1. The pigment of any one of embodiments 1 to 9, exhibiting a color strength of at least 105 %, preferably at least 107 %, more preferably in the range of from 107 to 140 %, more preferably from 110 to 140 %, more preferably in the range of from 120 to 140 %, the color strength being determined relative the a reference material RM as described in Reference Example 3.

[0203] 11. The pigment of any one of embodiments 1 to 10, preferably of embodiment 10, exhibiting a hue angle h° of at least 90, preferably in the range of from 90 to 95, more preferably from 91 to 95, more preferably from 91 to 95, the hue angle h° being determined as described in Reference Example 2.

[0204] 12. The pigment of any one of embodiments 1 to 11, preferably of embodiment 10 and 11, exhibiting a chroma value C* of at least 90, preferably at least 91, more preferably at least 92, more preferably in the range of from 92 to 97, more preferably in the range of from 92 to 96, the chroma value C* being determined as described in Reference Example 2.

[0205] 13. The pigment of any one of embodiments 1 to 12, preferably of embodiment 10, 11 and 12, exhibiting a lightness value L* of at least 80, preferably at least 81, more preferably at least 82, more preferably in the range of from 82 to 87, more preferably from 82 to 86, the lightness value L* being determined as described in Reference Example 2.

[0206] 14. The pigment of any one of embodiments 1 to 13, exhibiting a color strength in the range of from 130 to 140 %, a hue angle h° in the range of from 93 to 95, a chroma value C* in the range of from 95 to 96, and a lightness value L* in the range of from 85 to 86.

[0207] 15. A process for preparing a bismuth vanadate pigment, preferably a bismuth vanadate pigment according to any one of embodiments 1 to 14, the process comprising

[0208] (i) preparing a pigment core doped with one or more of phosphorus, magnesium, calcium, and aluminium, comprising

[0209] (1.1) preparing a bismuth vanadate pigment core precursor, comprising preparing an aqueous mixture from a bismuth reactant, a vanadate reactant and optionally a phosphorous dopant reactant, and precipitating said pigment core precursor from said aqueous mixture, obtaining an aqueous suspension comprising the pigment core precursor;

[0210] (1.2) adding one or more of a calcium dopant reactant, a magnesium dopant reactant, an aluminium dopant reactant and optionally a phosphorous dopant reactant to the aqueous suspension obtained according to (i.l), obtaining an aqueous mixture, and precipitating the pigment core doped with one or more of calcium, magnesium, aluminium and phosphorus from said aqueous mixture, obtaining an aqueous suspension comprising the doped pigment core; (i.3) separating the doped pigment core from the aqueous suspension obtained according to (i.2);

[0211] (ii) coating the doped pigment core obtained according to (i.3), comprising

[0212] (11.1) preparing an aqueous mixture comprising the doped pigment core obtained according to (i.3), one or more of a phosphorous coating reactant, an aluminium coating reactant, a calcium coating reactant and a magnesium coating reactant under coating conditions, obtaining an aqueous suspension comprising the doped pigment core coated with an oxidic coating precursor comprising one or more of magnesium, calcium, aluminium and phosphorous;

[0213] (11.2) separating the doped pigment core coated with the oxidic coating precursor from the suspension prepared according to (ii.l);

[0214] (iii) subjecting the doped pigment core coated with the oxidic coating precursor obtained according to (ii.2) to heat-treatment, obtaining the bismuth vanadate pigment, the pigment comprising a bismuth- and vanadium-containing core doped with one or more of magnesium, calcium, aluminium and phosphorus, the doped core being coated with an oxidic coating comprising one or more of magnesium, calcium, aluminium and phosphorous.

[0215] 16. The process of embodiment 15, wherein the bismuth reactant according to (i.1) comprises bismuth in oxidation state III, more preferably one or more Bi(III) salts, more preferably one or more of Bi(III) acetate and BI(III) nitrate, wherein more preferably, the bismuth reactant according to (i.l) comprises, more preferably consists of Bi(III) nitrate; wherein the bismuth reactant according to (i.l) is preferably employed as one or more aqueous solutions, more preferably one or more acidic aqueous solutions.

[0216] 17. The process of embodiment 15 or 16, wherein the vanadate reactant according to (i.l) comprises one or more of ammonium metavanadate, ammonium orthovanadate, ammonium polyvanadate, at least one alkali metal metavanadates, at least one alkali metal orthovanadates, and at least one alkali metal polyvanadates, preferably one or more of at least one alkali metal metavanadates, at least one alkali metal orthovanadates, and at least one alkali metal polyvanadates, more preferably one or more alkali metal metavanadates, more preferably one or more of potassium metavanadate and sodium metavanadate; wherein the vanadate reactant according to (i.l) is preferably employed as one or more aqueous solutions.

[0217] 18. The process of any one of embodiments 15 to 17, wherein according to (i.1), the bismuth reactant and the vanadate reactant are employed at a V : Bi elemental ratio in the range of from 0.7:1 to 1.3:1, preferably in the range of from 0.8:1 to 1.2:1, more preferably in the range of from 0.9:1 to 1.1:1.

[0218] 19. The process of any one of embodiments 15 to 18, wherein preparing a bismuth vanadate pigment core precursor according to (i.l) comprises preparing an aqueous mixture from a bismuth reactant, a vanadate reactant and a phosphorous dopant reactant, and precipitating said pigment core precursor from said aqueous mixture, obtaining an aqueous suspension comprising the pigment core precursor.

[0219] 20. The process of embodiment 19, wherein the phosphorous dopant reactant according to (i.l) comprises one or more of phosphate ions and hydrogen phosphate ions, the phosphorous dopant reactant according to (i.l) preferably comprising one or more of phosphoric acid, at least one alkali metal phosphate and ammonium phosphate, more preferably comprising one or more of phosphoric acid and at least one of sodium phosphate and ammonium phosphate, wherein more preferably, the phosphorous dopant reactant according to (i.l) comprises, more preferably consists of phosphoric acid; wherein the phosphorous dopant reactant according to (i.l) is preferably employed as one or more aqueous solutions.

[0220] 21. The process of embodiment 19 or 20, wherein according to (i.l), the phosphorous dopant reactant are employed at a P : (Bi+V) elemental ratio in the range of from 0.05: 1 to 0.1: 1, preferably in the range of from 0.55:1 to 0.09:1, more preferably in the range of from 0.06:1 to 0.08:1.

[0221] 22. The process of any one of embodiment 15 to 21, wherein preparing a bismuth vanadate pigment core precursor according to (i.l) is carried out at a temperature of the aqueous mixture according to (i.l) of at most 20 °C, preferably at most 15 °C, more preferably at most 10 °C, more preferably less than 10 °C, in each case at ambient pressure.

[0222] 23. The process of any one of embodiment 15 to 22, wherein preparing a bismuth vanadate pigment core precursor according to (i.l) is carried out at a pH of the aqueous mixture according to (i.l) in the range of from -1 to 11, more preferably in the range of from 0 to to 10.

[0223] 24. The process of embodiment 23, wherein at the beginning of step (i.l), the pH of the aqueous mixture is in the range of from 9 to 11, preferably in the range of from 9 to 10, and wherein at the end of step (i.l), the pH of the aqueous mixture is in the range of from - 1 to 2, preferably in the range of from 0 to 1. 25. The process of embodiment 23 or 24, wherein according to (i.l), the pH of the aqueous mixture in the range of from 9 to 11, preferably from 9 to 10, is adjusted to said values using at least one base, preferably comprising one or more of ammonium hydroxide and at least one alkali metal hydroxide, wherein more preferably, the at least one base comprises, more preferably consists of sodium hydroxide.

[0224] 26. The process of any one embodiments 15 to 25, wherein during (i.l), at least one acid is added to the aqueous mixture according, the at least one acid preferably being one or more of sulphuric acid and nitric acid, wherein more preferably, the at least one acid comprises, more preferably consists of nitric acid.

[0225] 27. The process of any one of embodiments 15 to 26, wherein the calcium dopant reactant according to (i.2) comprises at least one calcium salt, preferably one or more of calcium nitrate, calcium sulphate, calcium chloride, calcium carbonate, calcium hydroxide, and calcium acetate, wherein more preferably, the calcium dopant reactant according to (i.2) comprises, more preferably consists of calcium hydroxide.

[0226] 28. The process of any one of embodiments 15 to 27, wherein the magnesium dopant reactant according to (i.2) comprises at least one magnesium salt, preferably one or more of magnesium nitrate, magnesium sulphate, magnesium chloride, magnesium carbonate, magnesium hydroxide, and magnesium acetate, wherein more preferably, the magnesium dopant reactant according to (i.2) comprises, more preferably consists of magnesium hydroxide.

[0227] 29. The process of any one of embodiments 15 to 28, wherein the aluminium dopant reactant according to (i.2) comprises at least one aluminium containing salt, preferably one or more of aluminium nitrate, aluminium sulphate, aluminium carbonate, aluminium hydroxide, aluminium acetate, sodium aluminate, and potassium aluminate, wherein more preferably, the aluminium dopant reactant according to (i.2) comprises, more preferably consists of aluminium nitrate.

[0228] 30. The process of any one of embodiments 15 to 29, wherein the phosphorous dopant reactant according to (i.2) comprises one or more of phosphate ions and hydrogen phosphate ions, the phosphorous dopant reactant according to (i.2) preferably comprising one or more of phosphoric acid, at least one alkali metal phosphate and ammonium phosphate, more preferably comprising one or more of phosphoric acid and at least one of sodium phosphate and ammonium phosphate, wherein more preferably, the phosphorous dopant reactant according to (i.2) comprises, more preferably consists of phosphoric acid. 31. The process of any one of embodiments 27 to 30, wherein according to (i.2) , two or more, preferably three or more of a calcium dopant reactant, a magnesium dopant reactant, an aluminium dopant reactant and optionally a phosphorous dopant reactant are added to the aqueous suspension obtained according to (i.l), wherein more preferably according to (i.2), a calcium dopant reactant, a magnesium dopant reactant, and an aluminium dopant reactant are added to the aqueous suspension obtained according to (i.l).

[0229] 32. The process of embodiment 31, wherein according to (i.2), the aluminium dopant reactant is employed at a Al : (Bi+V) elemental ratio in the range of from 0.003:1 to 0.015:1, preferably in the range of from 0.006:1 to 0.012:1, more preferably in the range of from 0.008:1 to 0.010:1.

[0230] 33. The process of embodiment 31 or 32, wherein according to (i.2), the calcium dopant reactant is employed at a Ca : (Bi+V) elemental ratio in the range of from 0.005:1 to 0.050:1, preferably in the range of from 0.010:1 to 0.030:1, more preferably in the range of from 0.015:1 to 0.025:1.

[0231] 34. The process of any one of embodiments 31 to 33, wherein according to (i.2), the magnesium dopant reactant is employed at a Mg : (Bi+V) elemental ratio in the range of from 0.001:1 to 0.03:1, preferably in the range of from 0.002:1 to 0.02:1, more preferably in the range of from 0.005:1 to 0.015:1.

[0232] 35. The process of any one of embodiments 14 to 34, wherein according to (i.2), precipitating the pigment core doped with one or more of calcium, magnesium, aluminium and phosphorus comprise heating the aqueous mixture to a temperature of at least 80 °C, preferably at least 85 °C, more preferably at least 90 °C, more preferably at least 95 °C, in each case at ambient pressure.

[0233] 36. The process of any one of embodiments 15 to 35, wherein for precipitating the pigment core doped with one or more of calcium, magnesium, aluminium and phosphorus according to (i.2), the pH of the aqueous mixture is adjusted to a value in the range of from 3 to 6, preferably from 3.5 to 5.5, more preferably from 4 to 5.

[0234] 37. The process of embodiment 36, wherein according to (i.2), the pH of the aqueous mixture is adjusted to said values using at least one base, preferably comprising one or more of an alkali carbonate, an alkali hydrogen carbonate, an alkali hydroxide, and ammonia, preferably comprising one or more of an alkali carbonate, wherein more preferably, the at least one base comprises, more preferably consists of sodium carbonate. The process of any one of embodiments 15 to 37, wherein according to (i.3), separating the doped pigment core from the aqueous suspension comprises

[0235] (1.3.1) subjecting the aqueous suspension obtained according to (i.2), preferably after cooling to a temperature in the range of from 10 to 50 °C, preferably from 15 to 40 °C, more preferably from 20 to 30 °C, to solid-liquid separation, preferably to one or more of filtration and centrifugation, more preferably to filtration. The process of embodiment 38, wherein according to (i.3), separating the doped pigment core from the aqueous suspension further comprises, after (i.3.1),

[0236] (1.3.2) subjecting the doped pigment core separated by solid-liquid separation according to (i.3.1) to washing, preferably to washing with an aqueous medium, preferably water; wherein the washing according to (i.3.2) is preferably carried out until the obtained washing water exhibits a conductivity of at most 500 pS / cm. The process of embodiment 38 or 39, preferably of embodiment 39, wherein according to (i.3), separating the doped pigment core from the aqueous suspension further comprises after (i.3.1) or after (i.3.2), preferably after (i.3.2)

[0237] (1.3.3) subjecting the doped pigment core separated by solid-liquid separation according to (i.3.1), preferably the washed doped pigment core according to (i.3.2), to grinding, preferably to wet-milling; wherein the particle size of the ground doped pigment core is preferably in the range of from 0.1 to 2 pm, more preferably from 0.2 to 1.8 pm, more preferably from 0.3 to 1.6 pm, the particle size being determined as described in Reference Example 1. The process of any one of embodiments 15 to 40, wherein according to (ii.l), the phosphorous coating reactant comprises one or more of phosphate ions and hydrogen phosphate ions, the phosphorous coating reagent according to (ii.l) preferably comprising one or more of phosphoric acid, at least one alkali metal phosphate and ammonium phosphate, more preferably comprising one or more of phosphoric acid and at least one of sodium phosphate and ammonium phosphate, wherein more preferably, the phosphorous coating reactant according to (ii.l) comprises, more preferably consists of phosphoric acid. The process of any one of embodiments 15 to 41, wherein the aluminium coating reactant according to (ii.l) comprises at least one aluminium containing salt, preferably one or more of aluminium nitrate, aluminium sulphate, aluminium carbonate, aluminium hydroxide, aluminium acetate, sodium aluminate, and potassium aluminate, wherein more preferably, the aluminium coating reactant according to (ii.l) comprises, more preferably consists of aluminium sulphate.

[0238] 43. The process of any one of embodiments 15 to 42, wherein the calcium coating reactant according to (ii.l) comprises at least one calcium salt, preferably one or more of calcium nitrate, calcium sulphate, calcium chloride, calcium carbonate, calcium hydroxide, and calcium acetate, wherein more preferably, the calcium coating reactant according to (ii.1) comprises, more preferably consists of calcium nitrate.

[0239] 44. The process of any one of embodiments 15 to 43, wherein the magnesium coating reactant according to (ii.l) comprises at least one magnesium salt, preferably one or more of magnesium nitrate, magnesium sulphate, magnesium chloride, magnesium carbonate, magnesium hydroxide, and magnesium acetate, wherein more preferably, the magnesium coating reactant according to (ii.l) comprises, more preferably consists of magnesium nitrate.

[0240] 45. The process of any one of embodiments 15 to 44, wherein (ii.l) comprises preparing an aqueous mixture comprising the doped pigment core obtained according to (i.3), a phosphorous coating reactant and two or more of an aluminium coating reactant, a calcium coating reactant and a magnesium coating reactant under coating conditions, wherein more preferably, (ii.l) comprises preparing an aqueous mixture comprising the doped pigment core obtained according to (i.3), a phosphorous coating reactant, an aluminium coating reactant, a calcium coating reactant and a magnesium coating reactant under coating conditions.

[0241] 46. The process of any one of embodiments 15 to 45, wherein the coating conditions according to (ii.l) comprise a temperature of the aqueous mixture according to (ii.l) in the range of from 60 to 90 °C, preferably from 70 to 85 °C, more preferably from 75 to 85 °C, in each case at ambient pressure.

[0242] 47. The process of any one of embodiments 15 to 46, wherein the coating conditions according to (ii.l) comprise a pH of the aqueous mixture according to (ii.l) in the range of from 5 to 7, preferably from 5.5 to 7, more preferably from 6 to 6.5.

[0243] 48. The process of embodiment 47, wherein according to (ii.1), the pH of the aqueous mixture is adjusted to said values using at least one base, preferably comprising one or more of ammonium hydroxide and at least one alkali metal hydroxide, wherein more preferably, the at least one base comprises, more preferably consists of sodium hydroxide. 49. The process of any one of embodiments 15 to 48, wherein according to (ii.1), the aqueous mixture is prepared by adding two or more of the aluminium coating reactant, the calcium coating reactant and the magnesium coating in subsequent steps.

[0244] 50. The process of embodiment 49, wherein (ii.l) comprises

[0245] (11.1.1) preparing a first aqueous mixture comprising a first coating reactant;

[0246] (ii.1.2) adding a second coating reactant to the first aqueous mixture, obtaining a second aqueous mixture;

[0247] (ii.l.3) optionally or preferably adding a third coating reactant to the first aqueous mixture, obtaining a third aqueous mixture; wherein in at least one of steps (ii.1.1), (ii.l.2) and (ii.1.3), preferably in at least two of steps (ii.1.1), (ii.l.2) and (ii.1.3), more preferably in at least steps (ii.l.2) and (ii.1.3), a phosphorous coating reactant is added.

[0248] 51. The process of embodiment 50, wherein the pH of the first aqueous mixture according to

[0249] (11.1) is adjusted to a value in the range of from 5 to 7, preferably from 5.5 to 7, more preferably from 6 to 6.5, said adjusting comprising adding at least one base, preferably comprising one or more of ammonium hydroxide and at least one alkali metal hydroxide, wherein more preferably, the at least one base comprises, more preferably consists of sodium hydroxide.

[0250] 52. The process of embodiment 50 or 51, wherein the first coating reactant comprises, preferably consists of the aluminium coating reactant, the second coating reactant comprises, preferably consists of the calcium coating reactant, and the third coating reactant comprises, preferably consists of the magnesium coating reactant.

[0251] 53. The process of any one of embodiments 15 to 52, wherein according to (ii.l), the aluminium coating reactant is employed at a Al : (Bi+V) elemental ratio in the range of from 0.002:1 to 0.1:1, preferably in the range of from 0.005:1 to 0.09:1, more preferably in the range of from 0.009: 1 to 0.08: 1, wherein (Bi+V) refers to the amount of Bi and V comprised in the doped pigment core employed in (ii.l).

[0252] 54. The process of any one of embodiments 15 to 53, wherein according to (ii.1), the calcium coating reactant is employed at a Ca : (Bi+V) elemental ratio in the range of from 0.001 : 1 to 0.08:1, preferably in the range of from 0.002:1 to 0.07:1, more preferably in the range of from 0.005:1 to 0.06:1, wherein (Bi+V) refers to the amount of Bi and V comprised in the doped pigment core employed in (ii.1). 55. The process of any one of embodiments 15 to 54, wherein according to (ii.l), the magnesium coating reactant is employed at a Mg : (Bi+V) elemental ratio in the range of from 0.001:1 to 0.07:1, preferably in the range of from 0.002:1 to 0.06:1, more preferably in the range of from 0.004: 1 to 0.055 : 1 , wherein (Bi+V) refers to the amount of Bi and V comprised in the doped pigment core employed in (ii.l).

[0253] 56. The process of any one of embodiments 15 to 55, wherein according to (ii.l), the phosphorous coating reactant is employed at a P : (Bi+V) elemental ratio in the range of from 0.002:1 to 0.2:1, preferably in the range of from 0.005:1 to 0.19:1, more preferably in the range of from 0.01:1 to 0.18:1, wherein (Bi+V) refers to the amount of Bi and V comprised in the doped pigment core employed in (ii.l).

[0254] 57. The process of any one of embodiments 15 to 56, wherein according to (ii.2), separating the doped pigment core coated with the oxidic coating precursor from the aqueous suspension comprises

[0255] (11.2.1) subjecting the aqueous suspension obtained according to (ii.l), preferably after cooling to a temperature in the range of from 10 to 50 °C, preferably from 15 to 40 °C, more preferably from 20 to 30 °C, to solid-liquid separation, preferably to one or more of filtration and centrifugation, more preferably to filtration.

[0256] 58. The process of embodiment 57, wherein according to (ii.2), separating the doped pigment core coated with the oxidic coating precursor from the aqueous suspension further comprises, after (ii.2.1),

[0257] (11.2.2) subjecting the doped pigment core coated with the oxidic coating precursor separated by solid- liquid separation according to (ii.2.1) to washing, preferably to washing with an aqueous medium, preferably water; wherein the washing according to (ii.2.2) is preferably carried out until the obtained washing water exhibits a conductivity of at most 500 pS / cm.

[0258] 59. The process of embodiment 57 or 58, preferably of embodiment 58, wherein according to (ii.2), separating the doped pigment core coated with the oxidic coating precursor from the aqueous suspension further comprises after (ii.2.1) or after (ii.2.2), preferably after

[0259] (11.2.2)

[0260] (11.2.3) subjecting the doped pigment core coated with the oxidic coating precursor separated by solid-liquid separation according to (ii.2.1), preferably the washed doped pigment core coated with the oxidic coating precursor according to (ii.2.2), to grinding, preferably to wet-milling;

[0261] (11.2.4) optionally or preferably subjecting the ground doped pigment core coated with the oxidic coating precursor to deagglomeration; wherein the particle size of the obtained doped pigment core coated with the oxidic coating precursor is preferably in the range of from 0.1 to 2 pm, more preferably from 0.2 to 1.8 pm, more preferably from 0.3 to 1.6 pm, the particle size being determined as described in Reference Example 1. The process of any one of embodiments 15 to 59, wherein subjecting the doped pigment core coated with the oxidic coating precursor obtained according to (ii.3) to heattreatment comprises

[0262] (111.1) subjecting the doped pigment core coated with the oxidic coating precursor obtained according to (ii.3) to drying, preferably at a temperature in the range of from 90 to 175 °C, more preferably from 105 to 150 °C, more preferably from 110 to 130 °C, in each case at ambient pressure;

[0263] (111.2) subjecting the dried doped pigment core coated with the oxidic coating precursor obtained according to (iii.1) to calcination, preferably at a temperature in the range of from 450 to 650 °C, more preferably from 500 to 600 °C, more preferably from 525 to 575 °C, in each case at ambient pressure, obtaining the bismuth vanadate pigment comprising a bismuth- and vanadium-containing core doped with one or more of magnesium, calcium, aluminium and phosphorus, the doped core being coated with an oxidic coating comprising one or more of magnesium, calcium, aluminium and phosphorous. The process of any one of embodiments 15 to 60, further comprising, after (iii),

[0264] (iv) subjecting the bismuth vanadate pigment obtained according to (iii) to grinding, preferably to one or more of wet-milling and dry-milling; wherein the particle size of the ground bismuth vanadate pigment is preferably in the range of from 0.1 to 2 pm, more preferably from 0.2 to 1.8 pm, more preferably from 0.3 to 1.6 pm. The process of embodiment 60, wherein (iv) comprises subjecting the bismuth vanadate pigment obtained according to (iii) to dry-milling, the process further comprising, after

[0265] (iv),

[0266] (v) suspending the dry-milled bismuth vanadate pigment in water, and subjecting the obtained aqueous suspension to agitation, preferably mechanical agitation, more preferably stirring;

[0267] (vi) subjecting the stirred aqueous suspension obtained from (v) to drying, preferably at a temperature in the range of from 100 to 175 °C, more preferably from 105 to 150 °C, more preferably from 110 to 130 °C, in each case at ambient pressure, obtaining the dried bismuth vanadate pigment; (vii) optionally or preferably subjecting the dried bismuth vanadate pigment to deagglomeration .

[0268] 63. A bismuth vanadate pigment comprising a bismuth- and vanadium-containing core doped with one or more of magnesium, calcium, aluminium and phosphorus, the doped core being coated with an oxidic coating comprising one or more of magnesium, calcium, aluminium and phosphorous, obtainable or obtained by a process according to any one embodiments 15 to 62.

[0269] 64. The pigment of embodiment 63, wherein the oxidic coating comprises two or more of magnesium, calcium, aluminium and phosphorous, preferably three or more of magnesium, calcium, aluminium and phosphorous, more preferably magnesium, calcium, aluminium and phosphorous.

[0270] 65. The pigment of embodiment 63 or 64, wherein the oxidic coating comprises one or more of magnesium oxide, magnesium phosphate, calcium oxide, calcium phosphate, aluminium oxide and aluminium phosphate.

[0271] 66. The pigment of any one of embodiments 63 to 65, wherein the bismuth- and vanadium- containing core is doped with two or more of magnesium, calcium, aluminium and phosphorus, preferably with three or more of magnesium, calcium, aluminium and phosphorus, more preferably with magnesium, calcium, aluminium and phosphorus.

[0272] 67. The pigment of any one of embodiments 63 to 66, characterized by a composition according to formula (I)

[0273] Bi MgaAlbCacVdPeOf (I) wherein

[0274] 0.025 < a < 0.20; preferably 0.025 < a < 0.15; more preferably 0.025 < a < 0.10;

[0275] 0.025 < b < 0.20; preferably 0.025 < b < 0.15; more preferably 0.025 < b < 0.10;

[0276] 0.045 < c < 0.30; preferably 0.045 < c < 0.28; more preferably 0.045 < c < 0.26;

[0277] 0.50 < d < 2.0; preferably 0.60 < d < 1.9; more preferably 0.65 < d < 1.8; wherein e and f denote the number of phosphorous and oxygen atoms for satisfying the valence requirements of formula (I); wherein preferably 0.1 < e < 0.5; more preferably 0.13 < e < 0.45; more preferably 0.15 < e < 0.4.

[0278] 68. The pigment of any one of embodiments 63 to 67, characterized by a silicon content of at most 2000 weight-ppm, preferably at most 1500 weight-ppm, more preferably at most 1000 weight-ppm, calculated as elemental Si, wherein more preferably, the pigment is substantially free of silicon.

[0279] 69. The pigment of any one of embodiments 63 to 68, characterized by a molybdenum content of at most 1500 weight-ppm, preferably at most 1000 weight-ppm, more preferably at most 800 weight-ppm, calculated as elemental Mo, wherein more preferably, the pigment is substantially free of molybdenum.

[0280] 70. The pigment of any one of embodiments 63 to 69, characterized by a zinc content of at most 2000 weight-ppm, preferably at most 1500 weight-ppm, more preferably at most 1000 weight-ppm, calculated as elemental Zn, wherein more preferably, the pigment is substantially free of zinc.

[0281] 71. The pigment of any one of embodiments 63 to 70, being in particulate form, exhibiting a particle size in the range of from 0.2 to 3.0 pm, preferably from 0.25 to 2 pm, more preferably from 0.3 to 1.4 pm, the particle size being determined as described in Reference Example 1.

[0282] 72. The pigment of any one of embodiments 63 to 71, exhibiting a color strength of at least 105 %, preferably at least 107 %, more preferably in the range of from 107 to 140 %, more preferably from 110 to 140 %, more preferably in the range of from 120 to 140 %, the color strength being determined relative the a reference material RM as described in Reference Example 3.

[0283] 73. The pigment of any one of embodiments 63 to 72, preferably of embodiment 72, exhibiting a hue angle h° of at least 90, preferably in the range of from 90 to 95, more preferably from 91 to 95, more preferably from 91 to 95, the hue angle h° being determined as described in Reference Example 2.

[0284] 74. The pigment of any one of embodiments 63 to 73, preferably of embodiment 72 and 73, exhibiting a chroma value C* of at least 90, preferably at least 91, more preferably at least 92, more preferably in the range of from 92 to 97, more preferably in the range of from 92 to 96, the chroma value C* being determined as described in Reference Example 2.

[0285] 75. The pigment of any one of embodiments 63 to 74, preferably of embodiment 72, 73 and 74, exhibiting a lightness value L* of at least 80, preferably at least 81, more preferably at least 82, more preferably in the range of from 82 to 87, more preferably from 82 to 86, the lightness value L* being determined as described in Reference Example 2. The pigment of any one of embodiments 63 to 75, exhibiting a color strength in the range of from 130 to 140 %, a hue angle h° in the range of from 93 to 95, a chroma value C* in the range of from 95 to 96, and a lightness value L* in the range of from 85 to 86. A composition, comprising the pigment according to any one of embodiments 1 to 14 and / or according to any one of embodiments 63 to 76, the composition preferably being selected from the group consisting of coating compositions, paints, printing inks, liquid inks, plastics, films, fibers, glazes, and automotive paints. A method for increasing the color strength of a pigment composition comprising a bismuth- and vanadium-containing core, said core being coated with an oxidic coating comprising one or more of magnesium, calcium, aluminium and phosphorous, the method comprising doping said core, prior to coating, with one or more of magnesium, calcium, aluminium and phosphorus. Use of one or more of magnesium, calcium, aluminium and phosphorus as a bismuth- and vanadium-containing core doping agent for increasing the color strength of a pigment composition comprising said bismuth- and vanadium-containing core, the core being coated with an oxidic coating comprising one or more of magnesium, calcium, aluminium and phosphorous. The method and / or the use of embodiment 78 or 79, wherein two or more of magnesium, calcium, aluminium and phosphorus, preferably three or more of magnesium, calcium, aluminium and phosphorus, more preferably magnesium, calcium, aluminium and phosphorus are employed as core doping agent. The method and / or the use of any one of embodiments 78 to 80, the core being coated with an oxidic coating comprising two or more of magnesium, calcium, aluminium and phosphorous, preferably three or more of magnesium, calcium, aluminium and phosphorous, more preferably magnesium, calcium, aluminium and phosphorous. The method and / or the use of any one of embodiments 78 to 81 , wherein the color strength is increased by at least 5 %, preferably at least 10 %, more preferably at least 15 %, more preferably at least 20 %, more preferably at least 25 %, more preferably at least 30 %, in each case based on the color strength of the non-doped pigment composition. A method for increasing the color strength of a pigment composition comprising a bismuth- and vanadium-containing core, said core being doped with one or more of magnesium, calcium, aluminium and phosphorus, the method comprising coating the doped core with an oxidic coating comprising one or more of magnesium, calcium, aluminium and phosphorous.

[0286] 84. Use of an oxidic coating comprising one or more of magnesium, calcium, aluminium and phosphorous as doped core coating for increasing the color strength of a pigment composition comprising a bismuth- and vanadium-containing core, said core being doped with one or more of magnesium, calcium, aluminium and phosphorus.

[0287] 85. The method and / or the use of embodiment 83 or 84, wherein the oxidic coating comprises two or more of magnesium, calcium, aluminium and phosphorous, preferably three or more of magnesium, calcium, aluminium and phosphorous, more preferably magnesium, calcium, aluminium and phosphorous.

[0288] 86. The method and / or the use of any one of embodiments 83 to 85, wherein the core is doped with two or more of magnesium, calcium, aluminium and phosphorus, preferably with three or more of magnesium, calcium, aluminium and phosphorus, more preferably with magnesium, calcium, aluminium and phosphorus.

[0289] 87. The method and / or the use of any one of embodiments 83 to 86, wherein the color strength is increased by at least 2 %, preferably at least 3 %, more preferably at least 4 %, more preferably at least 5 %, more preferably at least 6 %, more preferably at least 7 %, in each case based on the color strength of the non-coated pigment composition.

[0290] 88. The use and / or the method of any one of embodiments 76 to 87, wherein the pigment composition exhibiting the increased color strength is prepared according to a process according to any one of embodiments 15 to 62.

[0291] 89. The use and / or the method of any one of embodiments 76 to 88, wherein the pigment composition exhibiting the increased color strength exhibits the features as defined in any one of embodiments 5 to 14.

[0292] 90. The use and / or the method of any one of embodiments 76 to 89, wherein the pigment composition exhibiting the non-increased color strength exhibits one or more, preferably two or more, more preferably all of the following features: a hue angle h° of at least 90, preferably in the range of from 90 to 95, more preferably from 91 to 95, more preferably from 91 to 94, the hue angle h° being determined as described in Reference Example 2; a chroma value C* of at least 90, preferably at least 91, more preferably at least 92, more preferably in the range of from 92 to 97, more preferably in the range of from 92 to 96, the chroma value C* being determined as described in Reference Example 2; a lightness value L* of at least 80, preferably at least 81, more preferably at least 82, more preferably in the range of from 82 to 87, more preferably from 82 to 86, the lightness value L* being determined as described in Reference Example 2.

[0293] The present invention has been described in detail, including various embodiments thereof. However, it will be appreciated that those skilled in the art, upon consideration of the present disclosure, may make modifications and / or improvements on this invention that fall within the scope and spirit of the invention.

[0294] Examples

[0295] The invention is further described by the following non-limiting examples which further illustrate the invention, and are not intended, nor should they be interpreted to, limit the scope of the invention.

[0296] Reference Examples - Measurement methods

[0297] Reference Example 1: Determination of particle sizes

[0298] Particle sizes were determined according to DIN 13320.

[0299] Reference Example 2: Determination of the values of L*, C*, and h°

[0300] The CIE L*C*h° color space corresponds to the CIE L*a*b* color space, the latter being determined according to DIN EN ISO 11664-4, wherein, however, in the CIE L*C*h° color space, the color values are given in polar coordinates. In the CIE L*a*b* color space, each perceptible color is defined in a three-dimensional coordinate system. For the measurement, both the illumination (light type and angle) and the measurement geometry are decisive. With the d8° / 0° geometry used according to the present invention, a circular directional illumination at a 8° angle and a view perpendicular to the same plane (0°) are realized. This takes the influence of the surface structure into account. By standard, samples are illuminated with D65 daylight beneath 10 ° normal observers.

[0301] For determining the CIE L*a*b* values, masstone coating films obtained were measured using a calibrated CM-2500d by Konica Minolta. (The term “masstone”, sometimes also referred to as “full tone”, refers to the full, undiluted color of a pigment when it is applied thickly enough to completely cover a surface; it is used to describe the true color of a pigment in its most concentrated form.) The coating films were prepared as follows: a mixture of 15.0 g of each pigment and 35.0 g of a hydroxyl functional acrylic resin (a melamine-formaldehyde condensation resin consisting of 55.40 g Setal (70 % in Xylol), 26.70 g Luwipal 012 (58 % in butanol / xylol 3:2), 2 g Laropal A81, 2.5 g Solvesso 150, 0.01 g Addid 160, 2 g butanol, 11.39 g xylol ) was shaken on a shaking machine for 60 min with 70 g glass beads (1 mm in diameter), then applied using a 200 pm spiral drawdown bar on a chromated aluminum sheet (Alu-Cards by Leneta), flashed off and heated at 50 °C for 30 min and subsequently at 140 °C for 30 min.

[0302] Reference Example 3: Determination of the color strength

[0303] Using the white reduction panels, the color strength was measured in accordance with ISO 18314-2 (2015) or “Industrielle Farbpriifung” by Hans G. Volz by iterative matching of the color depth to the 1 / 3 depth of shade. The relative color strength was evaluated against the reference material RM according to Comparative Example A described hereinunder as its hue is close to the target hue of the discussed invention and aids to judge the performance of the invention compared to state-of-the-art bismuth vanadate pigments.

[0304] In particular, the color strength was determined via spectrophotometry in white reduction, i.e. a white pigment (titanium dioxide) was added. For the white reduction, a white lacquer was prepared as follows: 160.0 g titanium dioxide was mixed with 240.0 g of a hydroxyl functional acrylic resin (a melamine-formaldehyde condensation resin, the same resin as described in Reference Example 2 above) using a shaking machine for 60 min with 600 g glass beads (2 mm in diameter). 10.0 g of the white lacquer was then combined with 2.7 g of the respective pigment composition (the pigment compositions of the present invention and of the comparative examples), and then mixed in a Speedmixer for 60 seconds at 2000 rpm and subsequently applied using a 200 pm spiral drawdown bar on a black and white contrast cardboard (Leneta 2A-3 opacity chart), flashed off and heated at 50 °C for 30 min and subsequently at 140 °C for 30 min.

[0305] Based on the data, the color strength was calculated, in each case based on a reference material RM. The color strength of the reference material RM was defined as 100 %. According to the present invention, the pigment composition according to Comparative Example A as described hereinunder was used as the reference material RM.

[0306] Reference Example 4: Determination of the pH

[0307] When a pH value is mentioned in the context of the present invention, it is to be understood as having been determined using a pH-sensitive glass electrode.

[0308] Comparative Example A: No coating, metal-doped core

[0309] The pigment composition according to Comparative Example A was prepared essentially in accordance with example 4 of US 9,868,860, as follows:

[0310] A mixture of 1000 g of water, 297 g of aqueous sodium metavanadate solution (7 weight-% of V, calculated as elemental V), 21 g of HNO3 (65 weight-%) and 7 g of H3PO4 (85 weight-%) was provided with stirring. The mixture was cooled to 8 °C, and the pH decreased to 6.8 after about 5 min. 351 g of an acidic bismuth nitrate solution (23.75 weight-% of Bi, calculated as elemental Bi) were added to the mixture within 60 min, the pH dropped to 0.5 giving a beige suspension. A solution of 1.54 g of Ca(OH)2 (96 %) in 24 g of water and a solution of 0.4 g of MgO (100 %) in 34 g of water was added within 15 min. The pH was adjusted to 4.4 using 170 g of an aqueous NaOH solution (25 weight-%) within 1.5 hours and then maintained at 4.6 using NaOH (5 weight-%).

[0311] A solution of 4 g of A1(NO3)3.9H2O (98 %) in 33 g of water was then added within 5 min. The mixture was heated at 95 °C for 83 min while maintaining a constant pH, and then cooled to room temperature. Any pH changes were adjusted using NaOH (5 weight-%). The yellow product was filtered, washed and dried.

[0312] The filter cake was then wet-milled in water to a particle size of about 1.24 pm and dried at 115 °C, followed by calcination at 550 °C for 1 hour and wet-milling again to a particle size of about 0.9 pm.

[0313] Comparative Example B: Non-metal-doped core, oxidic coating

[0314] A mixture of 524 g of water, 293 g of an aqueous sodium vanadate solution (7 weight-% of V, calculated as elemental V), 22 g of nitric acid (65 weight-% strength) and 3.4 g of phosphoric acid (75 weight-% strength) was provided with stirring. The temperature of said mixture was kept below 10 °C and the pH was kept above 9 by adding an aqueous solution of sodium hydroxide (25 weight-% strength). 349 g of an aqueous acidic bismuth nitrate solution (24 weight-% of Bi, calculated as elemental Bi) were added within 60 min.

[0315] The pH of the mixture was then adjusted to 4.5 by adding the sodium hydroxide solution. The mixture was then heated to a temperature of 95 °C while maintaining pH 4.5. After 90 min the suspension turned deep yellow, and the pH rose. The slurry was stirred at 95 °C until a constant pH was reached. After cooling to room temperature, the product was filtered off, washed salt- free and wet-milled to a particle size of about 0.8 pm.

[0316] The milled slurry was then transferred into a reaction vessel again to continue with the coating process. The volume of the slurry was filled up to 2000 g using water and its temperature was maintained at 80 °C over the entire process. 134 g of aluminium sulphate in water (i.e. 18.58 g Ah(SO4)3*14 H2O diluted in water) were added to the slurry within 90 min while the pH was maintained at 6.5 using the sodium hydroxide solution. Subsequently 133 g of calcium nitrate in water (3.43 g Ca(OH)2 and 11.56 g HNO3 diluted in water) and 124 g phosphoric acid (5%) were added within 90 min while the pH was maintained at 6.0. Finally, 109 g magnesium nitrate in water (2.47 g Mg(OH)2 and 12.84 g HNO3 diluted in water) and 124 g phosphoric acid were added within 90 min while the pH was maintained at 6.0. After cooling to room temperature, the product was filtered off, washed salt-free and wet milled to a particle size of about 0.8 to 1 pm.

[0317] The product was then dried at 120 °C in a through-circulation drying oven. The product was then deagglomerated using a mixer and subsequently heat-treated at 550 °C for 1 hour. The calcined product was then wet-milled again to an average particle size of about 0.5 to 1 pm, dried at 120 °C, and further deagglomerated with mixing.

[0318] Inventive Example 1

[0319] A mixture of 700 g of water, 294 g of an aqueous sodium metavanadate solution (7 weight-% of V, calculated as elemental V), 22 g of nitric acid (65 weight-% strength) and 8 g of phosphoric acid (75 weight-% strength) was provided with stirring. The temperature of said mixture was kept below 10 °C and the pH was kept above 9 by adding an aqueous solution of sodium hydroxide (25 weight-% strength). 354 g of an aqueous acidic bismuth nitrate solution (24 weight-% of Bi, calculated as elemental Bi) were added within 60 min.

[0320] 0.5 g magnesium hydroxide, 1.2 g calcium hydroxide and 2.9 g aluminium nitrate nonahydrate were added to the slurry while stirring. The pH of the mixture was then adjusted to 3.9 by adding the sodium hydroxide solution. The mixture was then heated to a temperature of 95 °C while maintaining pH 3.9. After 90 min the suspension turned deep yellow, and the pH rose. The slurry was stirred at 95 °C until a constant pH was reached. After cooling to room temperature, the product was filtered off, washed salt-free and wet- milled to a particle size of about 0.8 pm.

[0321] The milled slurry was then transferred into a reaction vessel again to continue with the coating process. The volume of the slurry was filled up to 2000 g using water and its temperature was maintained at 80 °C over the entire process. 134 g of aluminium sulphate in water (i.e. 18.58 g Ah(SO4)3*14 H2O diluted in water) was added to the slurry within 90 min while the pH was maintained at 6.5 using the sodium hydroxide solution. Subsequently 133 g of calcium nitrate in water (3.43 g Ca(OH)2 and 11.56 g HNO3 diluted in water) and 124 g phosphoric acid (5%) were added within 90 min while the pH was maintained at 6.0. Finally, 109 g magnesium nitrate in water (2.47 g Mg(OH)2 and 12.84 g HNO3 diluted in water) and 124 g phosphoric acid (5%) were added within 90 min while the pH was maintained at 6.0. After cooling to room temperature, the product was filtered off, washed salt-free and wet milled to a particle size of about 0.8 to 1 pm.

[0322] The product was then dried at 120 °C in a through-circulation drying oven. The product was then deagglomerated using a mixer and subsequently heat-treated at 550 °C for 1 hour. The calcined product was then wet-milled again, dried at 120 °C and further deagglomerated with mixing. The particles of the deagglomerated material exhibited an average particle size of about 0.5 to 0.7 pm.

[0323] Inventive Example 2: Using a different precipitation method than according to Example 1

[0324] For preparing the pigment composition according to the Inventive Example 2, the same respective solutions were used as described in Inventive Example 1.

[0325] A mixture of 770 g water, 389 g of the acidic bismuth solution, 24 g the nitric acid was provided with stirring. The temperature of said mixture was kept below 10 °C. A mixture of 323 g of the aqueous sodium metavanadate solution and 8.6 g phosphoric acid was then added within 60 min.

[0326] 0.6 g magnesium hydroxide, 1.3 g calcium hydroxide and 3.1 g aluminium nitrate nonahydrate were added to the slurry while stirring. The pH of the mixture was then adjusted to 4.2 by adding a sodium carbonate solution (15 weight- % strength). The mixture was then heated to a temperature of 95 °C while maintaining pH 4.2. After 60 min the pH rose. The slurry was stirred at 95 °C until a constant pH was reached. After cooling to room temperature, the product was filtered off, washed salt-free and wet-milled to a particle size of about 0.8 pm.

[0327] The milled slurry was then transferred into a reaction vessel again to continue with the coating process. The volume of the slurry was filled up to 2000 g using water and its temperature was maintained at 80 °C over the entire process. 67 g of aluminium sulphate in water (i.e. 9.29 g Ah(SO4)3*14 H2O diluted in water) were added to the slurry within 90 min while the pH was maintained at 6.5 using the sodium hydroxide solution. Subsequently, 67 g of calcium nitrate in water (1.73 g Ca(OH)2 and 5.83 g HNO3 diluted in water) and 62 g phosphoric acid (5%) were added within 90 min while the pH was maintained at 6.0. Finally, 55 g magnesium nitrate in water (1.25 g Mg(0H)2 and 6.48 g HNOa diluted in water) and 62 g phosphoric acid (5%) were added within 90 min while the pH was maintained at 6.0. After cooling to room temperature, the product was filtered off, washed salt-free and wet milled to a particle size of about 0.8 to 1 pm.

[0328] The product was then dried at 120 °C in a through-circulation drying oven. The product was then deagglomerated using a mixer and subsequently heat-treated at 550 °C for 1 hour. The calcined product was then wet-milled again, dried at 120 °C and further deagglomerated with mixing. The particles of the deagglomerated material exhibited an average particle size of about 0.5 to 0.7 pm.

[0329] Inventive Example 3: As Example 1, but smaller batch size and less coating material

[0330] A mixture of 630 g of water, 265 g of an aqueous sodium metavanadate solution (7 weight-% of V, calculated as elemental V), 20 g of nitric acid (65 weight-% strength) and 7.2 g of phosphoric acid (85 weight-% strength) was provided with stirring. The temperature of said mixture was kept below 10 °C and the pH was kept above 9 by adding an aqueous solution of sodium hydroxide (25 weight-% strength). 319 g of an acidic bismuth nitrate solution (24 weight-% of Bi, calculated as elemental Bi) were added within 60 min.

[0331] 0.5 g magnesium hydroxide, 1.1 g calcium hydroxide and 2.7 g aluminium nitrate nonahydrate were added to the slurry while stirring. The pH of the mixture was then adjusted to 3.9 by adding the sodium hydroxide solution. The mixture was then heated to a temperature of 95 °C while maintaining pH 3.9. After 90 min the suspension turned deep yellow, and the pH rose. The slurry was stirred at 95 °C until a constant pH was reached. After cooling to room temperature, the product was filtered off, washed salt-free and wet- milled to a particle size of about 0.8 pm.

[0332] The milled slurry was then transferred into a reaction vessel again to continue with the coating process. The volume of the slurry was filled up to 1800 g using water and its temperature was maintained at 80 °C over the entire process. 63 g of aluminium sulphate in water (i.e. 8.74 g Ah(SO4)3*14 H2O diluted in water) were added to the slurry within 90 min while the pH was maintained at 6.5 using the sodium hydroxide solution. Subsequently 63 g of calcium nitrate in water (1.63 g Ca(OH)2 and 5.5 g HNO3 diluted in water) and 56 g phosphoric acid (5%) were added within 90 min while the pH was maintained at 6.0. Finally, 50 g magnesium nitrate in water (1.13 g Mg(0H)2 and 5.89 g HNO3 diluted in water) and 56 g phosphoric acid (5%) were added within 90 min while the pH was maintained at 6.0. After cooling to room temperature, the product was filtered off, washed salt-free and wet milled to a particle size of about 0.8 to 1 pm. The product was then dried at 120 °C in a through-circulation drying oven. The product was then deagglomerated using a mixer and subsequently heat-treated at 550 °C for 1 hour. The calcined product was then wet-milled again, dried at 120 °C and further deagglomerated with mixing. The particles of the deagglomerated material exhibited an average particle size of about 0.5 to 0.7 pm.

[0333] Inventive Example 4: As Example 1, but less coating material than Example 1

[0334] A mixture of 700 g of water, 294 g of an aqueous sodium metavanadate solution (7 weight-% of V, calculated as elemental V), 22 g of nitric acid (65 weight-% strength) and 8 g of phosphoric acid (85 weight-% strength) was provided with stirring. The temperature of said mixture was kept below 10 °C and the pH was kept above 9 by adding an aqueous solution of sodium hydroxide (25 weight-% strength). 354 g of an acidic bismuth nitrate solution (24 weight-% of Bi, calculated as elemental Bi) were added within 60 min.

[0335] 0.5 g magnesium hydroxide, 1.2 g calcium hydroxide and 2.9 g aluminium nitrate nonahydrate were added to the slurry while stirring. The pH of the mixture was then adjusted to 3.9 by adding the sodium hydroxide solution. The mixture was then heated to a temperature of 95 °C while maintaining pH 3.9. After 90 min the suspension turned deep yellow, and the pH rose. The slurry was stirred at 95 °C until a constant pH was reached. After cooling to room temperature, the product was filtered off, washed salt-free and wet- milled to a particle size of about 0.8 pm.

[0336] The milled slurry was then transferred into a reaction vessel again to continue with the coating process. The volume of the slurry was filled up to 2000 g using water and its temperature was maintained at 80 °C over the entire process. 34 g of aluminium sulphate (i.e. 4.71 g Ah(SO4)3*14 H2O diluted in water) in water were added to the slurry within 90 min while the pH was maintained at 6.5 using the sodium hydroxide solution. Subsequently 34 g of calcium nitrate in water (0.88 g Ca(OH)2 and 2.9 g HNO3 diluted in water) and 31 g phosphoric acid (5%) were added within 90 min while the pH was maintained at 6.0. Finally, 28 g magnesium nitrate in water (0.63 g Mg(0H)2 and 4.01 g HNO3 diluted in water) and 31 g phosphoric acid (5%) were added within 90 min while the pH was maintained at 6.0. After cooling to room temperature, the product was filtered off, washed salt-free and wet milled to a particle size of about 0.8 to 1 pm.

[0337] The product was then dried at 120 °C in a through-circulation drying oven. The product was then deagglomerated using a mixer and subsequently heat-treated at 550 °C for 1 hour. The calcined product was then wet-milled again, dried at 120 °C and further deagglomerated with mixing. The particles of the deagglomerated material exhibited an average particle size of about 0.5 to 0.7 pm. Inventive Example 5: As Example 1, but less coating material than in Examples 1 and 4

[0338] A mixture of 700 g of water, 294 g of an aqueous sodium metavanadate solution (7 weight-% of V, calculated as elemental V), 22 g of nitric acid (65 weight-% strength) and 8 g of phosphoric acid (85 weight-% strength) was provided with stirring. The temperature of said mixture was kept below 10 °C and the pH was kept above 9 by adding an aqueous solution of sodium hydroxide (25 weight-% strength). 354 g of an acidic bismuth nitrate solution (24 weight-% of Bi, calculated as elemental Bi) were added within 60 min.

[0339] 0.5 g magnesium hydroxide, 1.2 g calcium hydroxide and 2.9 g aluminium nitrate nonahydrate were added to the slurry while stirring. The pH of the mixture was then adjusted to 3.9 by adding the sodium hydroxide solution. The mixture was then heated to a temperature of 95 °C while maintaining pH 3.9. After 90 min the suspension turned deep yellow, and the pH rose. The slurry was stirred at 95 °C until a constant pH was reached. After cooling to room temperature, the product was filtered off, washed salt-free and wet- milled to a particle size of about 0.8 pm.

[0340] The milled slurry was then transferred into a reaction vessel again to continue with the coating process. The volume of the slurry was filled up to 2000 g using water and its temperature was maintained at 80 °C over the entire process. 17 g of aluminium sulphate in water (2.36 g Ah(SO4)3*14 H2O diluted in water) was added to the slurry within 90 min while the pH was maintained at 6.5 using the sodium hydroxide solution. Subsequently 17 g of calcium nitrate in water (0.44 g Ca(OH)2 and 1.48 g HNO3 diluted in water) and 16 g phosphoric acid (5%) were added within 90 min while the pH was maintained at 6.0. Finally, 14 g magnesium nitrate in water (0.32 g Mg(OH)2 and 1.67 g HNO3 diluted in water) and 16 g phosphoric acid (5%) were added within 90 min while the pH was maintained at 6.0. After cooling to room temperature, the product was filtered off, washed salt-free and wet milled to a particle size of about 1 pm.

[0341] The product was then dried at 120 °C in a through-circulation drying oven. The product was then deagglomerated using a mixer and subsequently heat-treated at 550 °C for 1 hour. The calcined product was then wet-milled again, dried at 120 °C and further deagglomerated with mixing. The particles of the deagglomerated material exhibited an average particle size of about 0.5 to 0.7 pm.

[0342] Inventive Example 6: As Example 1, but less coating material than Examples 1, 4 and 5

[0343] A mixture of 700 g of water, 294 g of an aqueous sodium metavanadate solution (7 weight-% of V, calculated as elemental V), 22 g of nitric acid (65 weight-% strength) and 8 g of phosphoric acid (85 weight-% strength) was provided with stirring. The temperature of said mixture was kept below 10 °C and the pH was kept above 9 by adding an aqueous solution of sodium hydroxide (25 weight-% strength). 354 g of an acidic bismuth nitrate solution (24 weight-% of Bi, calculated as elemental Bi) were added within 60 min.

[0344] 0.5 g magnesium hydroxide, 1.2 g calcium hydroxide and 2.9 g aluminium nitrate nonahydrate were added to the slurry while stirring. The pH of the mixture was then adjusted to 3.9 by adding the sodium hydroxide solution. Afterwards 13 g of a Bi and V containing pigment intermediate was added to the mixture. The mixture was then heated to a temperature of 95 °C while maintaining pH 3.9. After 90 min the suspension turned deep yellow, and the pH rose. The slurry was stirred at 95 °C until a constant pH was reached. After cooling to room temperature, the product was filtered off, washed salt-free and wet- milled to a particle size of about 0.8 pm.

[0345] The milled slurry was then transferred into a reaction vessel again to continue with the coating process. The volume of the slurry was filled up to 2000 g using water and its temperature was maintained at 80 °C over the entire process. 13 g of aluminium sulphate in water (1.8 g Ah(SO4)3*14 H2O diluted in water) was added to the slurry within 90 min while the pH was maintained at 6.5 using the sodium hydroxide solution. Subsequently 13 g of calcium nitrate in water (0.34 g Ca(OH)2 and 1.15 g HNO3 diluted in water) and 12 g phosphoric acid (5%) were added within 90 min while the pH was maintained at 6.0. Finally, 11 g magnesium nitrate in water (0.25 g Mg(OH)2 and 1.31 g HNO3 diluted in water) and 12 g phosphoric acid (5%) were added within 90 min while the pH was maintained at 6.0. After cooling to room temperature, the product was filtered off, washed salt-free and wet milled to a particle size of about 1 pm.

[0346] The product was then dried at 120 °C in a through-circulation drying oven. The product was then deagglomerated using a mixer and subsequently heat-treated at 550 °C for 1 hour. The calcined product was then wet-milled again, dried at 120 °C and further deagglomerated with mixing. The particles of the deagglomerated material exhibited an average particle size of about 0.5 to 0.7 pm.

[0347] Inventive Example 7: Same as Example 5, except dry-milling after calcination

[0348] The same procedure was used as in Example 5, but a dry- milling grinding technique was used after the calcination step, using a AFG 400 from Hosokawa Alpine operating at 5000 rpm and 5 bar. The milled product exhibited an average particle size of about 0.3 to 0.5 pm.

[0349] Inventive Example 8: Same as Example 5, except dry-milling after calcination

[0350] The same procedure was used as in Example 5, but a dry- milling grinding technique was used after the calcination step, using a AFG 400 from Hosokawa Alpine operating at 6000 rpm and 7 bar. The milled product exhibited an average particle size of about 0.3 to 0.5 pm.

[0351] Inventive Example 9: Same as Example 7, with stirring in water

[0352] The same procedure was used as in Example 7, including an additional stirring of the milled product exhibited an average particle size of about 0.3 to 0.5 pm in water (about 5 g of product in 1000 ml water) for 2 h at ambient temperature and subsequent drying at 120 °C and subsequent deagglomerating. The product exhibited an average particle size of about 0.3 to 0.5 pm.

[0353] Inventive Example 10: Same as Example 8, with stirring in water

[0354] The same procedure was used as in Example 8, including an additional stirring of the milled product exhibited an average particle size of about 0.3 to 0.5 pm in water (about 5 g of product in 1000 ml water) for 2 h at ambient temperature and subsequent drying at 120 °C and subsequent deagglomerating. The product exhibited an average particle size of about 0.3 to 0.5 pm.

[0355] In the following Table 1 , the colorimetric strengths determined for the finally obtained pigments according to the Inventive Examples 1 to 6 and the Comparative Examples, are listed, together with the relative amounts of doping and coating compounds used for preparing the pigments, given with respect to elemental ratios of Bi, V, Mg, Ca, Al, and P, respectively:

[0356] Table 1

[0357] Color strengths (Co Str) and relative amounts of doping and coating agents according to the examples

[0358] 1 1different precipitation method and less coating material compared to Example 1

[0359] 2)as Example 1, but smaller batch size and less coating material compared to Example 1

[0360] 3)as Example 1, but less coating material compared to Example 1

[0361] 4)as Example 1, but less coating material compared to Examples 1 and 45)as Example 1, but less coating material compared to Examples 1, 4 and 5

[0362] 6)as Example 5, except dry-milling after calcination

[0363] 7)as Example 5, except dry-milling after calcination at different conditions than in Example 7

[0364] 8)as Example 7, with stirring in water of milled sample with subsequent drying

[0365] 9)as Example 8, with stirring in water of milled sample with subsequent drying

[0366] In the following Table 2, the colorimetric data determined for the finally obtained pigments according to the Inventive Examples and the Comparative Examples are shown:

[0367] Table 2 Colorimetric data obtained according to the examples

[0368]

[0369] As shown in Table 2, the Inventive Examples containing the combination of dopants and oxidic coatings show an increased color strength compared to Comparative Example A (bismuth yellow vanadate Example 5 from US 9,868,860), which also contains Mg, Ca and Al as a dopant but no additional oxidic coating; and Comparative Example B, which comprises an oxidic coating but no metal dopants. Thus, the combination of doping and coating of the present application enables higher color strength while maintaining high chroma and lightness values for a yellow bismuth vanadate.

[0370] In the following Table 3, results obtained according to the Inventive Examples 1 and 3 to 6 are summarized (the pigments according to these examples were prepared by the same method; Inventive Example 2 was prepared using a different precipitation method).

[0371] Table 3

[0372] Color strength values and coating composition according to Inventive Example 1 and 3-6 amount in the core

[0373] As shown in Table 3, it was surprisingly found that - while the presence of an oxidic coating is necessary in order to improve the color strength; reference is made, for example, to Table 2 above - there is the clear tendency that the lower the amount of coating material relative to Bi and V comprised in the doped core, the higher the (improved) color strength of the pigment.

Claims

Claims1. A bismuth vanadate pigment comprising a bismuth- and vanadium-containing core doped with one or more of magnesium, calcium, aluminium and phosphorus, the doped core being coated with an oxidic coating comprising one or more of magnesium, calcium, aluminium and phosphorous.

2. The pigment of claim 1 , wherein the oxidic coating comprises two or more of magnesium, calcium, aluminium and phosphorous, preferably three or more of magnesium, calcium, aluminium and phosphorous, more preferably magnesium, calcium, aluminium and phosphorous.

3. The pigment of claim 1 or 2, wherein the bismuth- and vanadium-containing core is doped with two or more of magnesium, calcium, aluminium and phosphorus, preferably with three or more of magnesium, calcium, aluminium and phosphorus, more preferably with magnesium, calcium, aluminium and phosphorus.

4. The pigment of any one of claims 1 to 3, characterized by a composition according to formula (I)Bi MgaAlbCacVdPeOf (I) wherein0.025 < a < 0.20; preferably 0.025 < a < 0.15; more preferably 0.025 < a < 0.10;0.025 < b < 0.20; preferably 0.025 < b < 0.15; more preferably 0.025 < b < 0.10;0.045 < c < 0.30; preferably 0.045 < c < 0.28; more preferably 0.045 < c < 0.26;0.50 < d < 2.0; preferably 0.60 < d < 1.9; more preferably 0.65 < d < 1.8; wherein e and f denote the number of phosphorous and oxygen atoms for satisfying the valence requirements of formula (I); wherein preferably 0.1 < e < 0.5; more preferably 0.13 < e < 0.45; more preferably 0.15 < e < 0.4.

5. The pigment of any one of claims 1 to 4, characterized by one or more of a silicon content of at most 2000 weight-ppm, preferably at most 1500 weight-ppm, more preferably at most 1000 weight-ppm, calculated as elemental Si, wherein more preferably, the pigment is substantially free of silicon; a molybdenum content of at most 1500 weight-ppm, preferably at most 1000 weight-ppm, more preferably at most 800 weight-ppm, calculated as elemental Mo, wherein more preferably, the pigment is substantially free of molybdenum; a zinc content of at most 2000 weight-ppm, preferably at most 1500 weight-ppm, more preferably at most 1000 weight-ppm, calculated as elemental Zn, whereinmore preferably, the pigment is substantially free of zinc.

6. The pigment of any one of claims 1 to 5, exhibiting a color strength of at least 105 %, preferably at least 107 %, more preferably in the range of from 107 to 140 %, more preferably from 110 to 140 %, more preferably in the range of from 120 to 140 %, the color strength being determined relative the a reference material RM as described in Reference Example 3; said pigment preferably exhibiting one or more of, more preferably two or more of, more preferably all of a hue angle h° of at least 90, preferably in the range of from 90 to 95, more preferably from 91 to 95, more preferably from 91 to 95; a chroma value C* of at least 90, preferably at least 91, more preferably at least 92, more preferably in the range of from 92 to 97, more preferably in the range of from 92 to 96; lightness value L* of at least 80, preferably at least 81, more preferably at least 82, more preferably in the range of from 82 to 87, more preferably from 82 to 86.

7. A process for preparing a bismuth vanadate pigment, preferably the bismuth vanadate pigment according to any one of claims 1 to 6, the process comprising(i) preparing a pigment core doped with one or more of phosphorus, magnesium, calcium, and aluminium, comprising(i.1) preparing a bismuth vanadate pigment core precursor, comprising preparing an aqueous mixture from a bismuth reactant, a vanadate reactant and optionally a phosphorous dopant reactant, and precipitating said pigment core precursor from said aqueous mixture, obtaining an aqueous suspension comprising the pigment core precursor;(1.2) adding one or more of a calcium dopant reactant, a magnesium dopant reactant, an aluminium dopant reactant and optionally a phosphorous dopant reactant to the aqueous suspension obtained according to (i.l), obtaining an aqueous mixture, and precipitating the pigment core doped with one or more of calcium, magnesium, aluminium and phosphorus from said aqueous mixture, obtaining an aqueous suspension comprising the doped pigment core;(1.3) separating the doped pigment core from the aqueous suspension obtained according to (i.2);(ii) coating the doped pigment core obtained according to (i.3), comprising(ii.l) preparing an aqueous mixture comprising the doped pigment core obtained according to (i.3), one or more of a phosphorous coating reactant, an aluminium coating reactant, a calcium coating reactant and a magnesiumcoating reactant under coating conditions, obtaining an aqueous suspension comprising the doped pigment core coated with an oxidic coating precursor comprising one or more of magnesium, calcium, aluminium and phosphorous;(ii.2) separating the doped pigment core coated with the oxidic coating precursor from the suspension prepared according to (ii.l);(iii) subjecting the doped pigment core coated with the oxidic coating precursor obtained according to (ii.2) to heat-treatment, obtaining the bismuth vanadate pigment, the pigment comprising a bismuth- and vanadium-containing core doped with one or more of magnesium, calcium, aluminium and phosphorus, the doped core being coated with an oxidic coating comprising one or more of magnesium, calcium, aluminium and phosphorous.

8. The process of claim 7, wherein according to (i.1 ), the bismuth reactant and the vanadate reactant are employed at a V : Bi elemental ratio in the range of from 0.7:1 to 1.3:1, preferably in the range of from 0.8:1 to 1.2:1, more preferably in the range of from 0.9:1 to 1.1:

1. the phosphorous dopant reactant is employed at a P : (Bi+V) elemental ratio in the range of from 0.05:1 to 0.1:1, preferably in the range of from 0.55:1 to 0.09:1, more preferably in the range of from 0.06:1 to 0.08:

1. the aluminium dopant reactant is employed at a Al : (Bi+V) elemental ratio in the range of from 0.003: 1 to 0.015: 1, preferably in the range of from 0.006: 1 to 0.01 : 1, more preferably in the range of from 0.008:1 to 0.010:

1. the calcium dopant reactant is employed at a Ca : (Bi+V) elemental ratio in the range of from 0.005: 1 to 0.050: 1, preferably in the range of from 0.010: 1 to 0.030: 1, more preferably in the range of from 0.015:1 to 0.025:

1. the magnesium dopant reactant is employed at a Mg : (Bi+V) elemental ratio in the range of from 0.001:1 to 0.03:1, preferably in the range of from 0.002:1 to 0.02:1, more preferably in the range of from 0.005:1 to 0.015:1.

9. The process of claim 7 or 8, wherein according to (i.3), separating the doped pigment core from the aqueous suspension comprises(i.3.1) subjecting the aqueous suspension obtained according to (i.2), preferably after cooling to a temperature in the range of from 10 to 50 °C, preferably from 15 to 40 °C, more preferably from 20 to 30 °C, to solid-liquid separation, preferably to one or more of filtration and centrifugation, more preferably to filtration; wherein according to (i.3), separating the doped pigment core from the aqueous suspension preferably further comprises, after (i.3.1),(1.3.2) subjecting the doped pigment core separated by solid-liquid separation according to (i.3.1) to washing, preferably to washing with an aqueous medium, preferably water; wherein separating the doped pigment core from the aqueous suspension more preferably further comprises after (i.3.1) or after (i.3.2), preferably after (i.3.2)(1.3.3) subjecting the doped pigment core separated by solid-liquid separation according to (i.3.1), preferably the washed doped pigment core according to (i.3.2), to grinding, preferably to wet-milling.

10. The process of any one of claims 7 to 9, wherein according to (ii.l), the aqueous mixture is prepared by adding two or more of the aluminium coating reactant, the calcium coating reactant and the magnesium coating in subsequent steps; wherein (ii.l) preferably comprises(ii.1.1) preparing a first aqueous mixture comprising a first coating reactant;(ii.1.2) adding a second coating reactant to the first aqueous mixture, obtaining a second aqueous mixture;(11.1.3) optionally or preferably adding a third coating reactant to the first aqueous mixture, obtaining a third aqueous mixture; wherein in at least one of steps (ii.1.1), (ii.l.2) and (ii.1.3), preferably in at least two of steps (ii.1.1), (ii.l.2) and (ii.1.3), more preferably in at least steps (ii.l.2) and (ii.1.3), a phosphorous coating reactant is added.

11. The process of any one of claims 7 to 10, wherein according to (ii.l), the aluminium coating reactant is employed at a Al : (Bi+V) elemental ratio in the range of from 0.002:1 to 0.1:1, preferably in the range of from 0.005:1 to 0.09:1, more preferably in the range of from 0.009:1 to 0.08:1, wherein (Bi+V) refers to the amount of Bi and V comprised in the doped pigment core employed in (ii.l); the calcium coating reactant is employed at a Ca : (Bi+V) elemental ratio in the range of from 0.001:1 to 0.08:1, preferably in the range of from 0.002:1 to 0.07:1, more preferably in the range of from 0.005:1 to 0.06:1, wherein (Bi+V) refers to the amount of Bi and V comprised in the doped pigment core employed in (ii.l); the magnesium coating reactant is employed at a Mg : (Bi+V) elemental ratio in the range of from 0.001:1 to 0.07:1, preferably in the range of from 0.002:1 to 0.06:1, more preferably in the range of from 0.004:1 to 0.055:1, wherein (Bi+V) refers to the amount of Bi and V comprised in the doped pigment core employed in (ii.l); the phosphorous coating reactant is employed at a P : (Bi+V) elemental ratio in the range of from 0.002:1 to 0.2:1, preferably in the range of from 0.005:1 to 0.19:1, more preferably in the range of from 0.01:1 to 0.18:1, wherein (Bi+V) refers to the amount of Bi and V comprised in the doped pigment core employed in (ii.1).

12. The process of any one of claims 7 to 11, wherein according to (ii.2), separating the doped pigment core coated with the oxidic coating precursor from the aqueous suspension comprises(11.2.1) subjecting the aqueous suspension obtained according to (ii.l), preferably after cooling to a temperature in the range of from 10 to 50 °C, preferably from 15 to 40 °C, more preferably from 20 to 30 °C, to solid-liquid separation, preferably to one or more of filtration and centrifugation, more preferably to filtration; wherein according to (ii.2), separating the doped pigment core coated with the oxidic coating precursor from the aqueous suspension preferably further comprises, after (ii.2.1),(11.2.2) subjecting the doped pigment core coated with the oxidic coating precursor separated by solid- liquid separation according to (ii.2.1) to washing, preferably to washing with an aqueous medium, preferably water; wherein according to (ii.2), separating the doped pigment core coated with the oxidic coating precursor from the aqueous suspension more preferably further comprises after(11.2.1) or after (ii.2.2), preferably after (ii.2.2)(11.2.3) subjecting the doped pigment core coated with the oxidic coating precursor separated by solid-liquid separation according to (ii.2.1), preferably the washed doped pigment core coated with the oxidic coating precursor according to(ii.2.2), to grinding, preferably to wet-milling;(11.2.4) optionally or preferably subjecting the ground doped pigment core coated with the oxidic coating precursor to deagglomeration.

13. The process of any one of claims 7 to 12, wherein subjecting the doped pigment core coated with the oxidic coating precursor obtained according to (ii.3) to heat-treatment comprises(111.1) subjecting the doped pigment core coated with the oxidic coating precursor obtained according to (ii.3) to drying, preferably at a temperature in the range of from 90 to 175 °C, more preferably from 105 to 150 °C, more preferably from 110 to 130 °C, in each case at ambient pressure;(111.2) subjecting the dried doped pigment core coated with the oxidic coating precursor obtained according to (iii.1) to calcination, preferably at a temperature in the range of from 450 to 650 °C, more preferably from 500 to 600 °C, more preferably from 525 to 575 °C, in each case at ambient pressure, obtaining the bismuth vanadate pigment comprising a bismuth- and vanadium-containing core doped with one or more of magnesium, calcium, aluminium and phosphorus, the doped core being coated with an oxidic coating comprising one or more of magnesium, calcium, aluminium and phosphorous.

14. The process of any one of claims 7 to 13, further comprising, after (iii),(iv) subjecting the bismuth vanadate pigment obtained according to (iii) to grinding, preferably to one or more of wet-milling and dry-milling; wherein if (iv) comprises subjecting the bismuth vanadate pigment obtained according to (iii) to dry-milling, the process preferably further comprising, after (iv),(v) suspending the dry-milled bismuth vanadate pigment in water, and subjecting the obtained aqueous suspension to agitation, preferably mechanical agitation, more preferably stirring;(vi) subjecting the stirred aqueous suspension obtained from (v) to drying, preferably at a temperature in the range of from 100 to 175 °C, more preferably from 105 to 150 °C, more preferably from 110 to 130 °C, in each case at ambient pressure, obtaining the dried bismuth vanadate pigment;(vii) optionally or preferably subjecting the dried bismuth vanadate pigment to deagglomeration .

15. A bismuth vanadate pigment comprising a bismuth- and vanadium-containing core doped with one or more of magnesium, calcium, aluminium and phosphorus, the doped core being coated with an oxidic coating comprising one or more of magnesium, calcium, aluminium and phosphorous, obtainable or obtained by a process according to any one of claims 7 to 14.

16. A composition, comprising the pigment according to any one of claims 1 to 6 and / or claim 15, the composition being selected from the group consisting of coating compositions, paints, printing inks, liquid inks, plastics, films, fibers, glazes, and automotive paints.

17. Use of one or more of magnesium, calcium, aluminium and phosphorus as a bismuth- and vanadium-containing core doping agent for increasing the color strength of a pigment composition comprising said bismuth- and vanadium-containing core, the core being coated with an oxidic coating comprising one or more of magnesium, calcium, aluminium and phosphorous, wherein preferably two or more of magnesium, calcium, aluminium and phosphorus, more preferably three or more of magnesium, calcium, aluminium and phosphorus, more preferably magnesium, calcium, aluminium and phosphorus are employed as core doping agent, and wherein the core is preferably coated with an oxidic coating comprising two or more of magnesium, calcium, aluminium and phosphorous, more preferably three or more of magnesium, calcium, aluminium and phosphorous, more preferably magnesium, calcium, aluminium and phosphorous; wherein the color strength is increased preferably by at least 5 %, more preferably at least 10 %, more preferably at least 15 %, more preferably at least 20 %, more preferably atleast 25 %, more preferably at least 30 %, in each case based on the color strength of the non-doped pigment composition.

18. Use of an oxidic coating comprising one or more of magnesium, calcium, aluminium and phosphorous as doped core coating for increasing the color strength of a pigment composition comprising a bismuth- and vanadium-containing core, said core being doped with one or more of magnesium, calcium, aluminium and phosphorus; wherein the oxidic coating preferably comprises two or more of magnesium, calcium, aluminium and phosphorous, preferably three or more of magnesium, calcium, aluminium and phosphorous, more preferably magnesium, calcium, aluminium and phosphorous; wherein the core is preferably doped with two or more of magnesium, calcium, aluminium and phosphorus, more preferably with three or more of magnesium, calcium, aluminium and phosphorus, more preferably with magnesium, calcium, aluminium and phosphorus; wherein the color strength is preferably increased by at least 2 %, more preferably at least 3 %, more preferably at least 4 %, more preferably at least 5 %, more preferably at least 6 %, more preferably at least 7 %, in each case based on the color strength of the noncoated pigment composition.

19. The use of claim 17 or 18, wherein the pigment composition exhibiting the non-increased color strength exhibits one or more, preferably two or more, more preferably all of the following features: a hue angle h° of at least 90, preferably in the range of from 90 to 95, more preferably from 91 to 95, more preferably from 91 to 94; a chroma value C* of at least 90, preferably at least 91, more preferably at least 92, more preferably in the range of from 92 to 97, more preferably in the range of from 92 to 96; a lightness value L* of at least 80, preferably at least 81, more preferably at least 82, more preferably in the range of from 82 to 87, more preferably from 82 to 86.

20. The use of any one of claims 17 to 19, wherein the pigment composition exhibiting the increased color strength exhibits one or more, preferably two or more, more preferably all of the following features: a hue angle h° of at least 90, preferably in the range of from 90 to 95, more preferably from 91 to 95, more preferably from 91 to 94; a chroma value C* of at least 90, preferably at least 91, more preferably at least 92, more preferably in the range of from 92 to 97, more preferably in the range of from 92 to 96; a lightness value L* of at least 80, preferably at least 81, more preferably at least 82, more preferably in the range of from 82 to 87, more preferably from 82 to 86.

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