DE102018101485A1 - Process for the preparation of pigment particles from mixed oxides containing manganese and zinc - Google Patents

Abstract

Process for the preparation of pigment particles from mixed oxides containing manganese and zinc, comprising the following steps: a. Forming precursor particles of manganese and zinc-containing mixed carbonates, by co-precipitation of manganese and zinc carbonates by adding a carbonate and / or bicarbonate salt to a first aqueous solution of a water-soluble bivalent zinc salt and a water-soluble bivalent manganese salt in a predetermined molar ratio of zinc salt to manganese salt, b. Isolating the precursor particles from the first solution, washing and drying them, andc. Firing the precursor particles to obtain the pigment particles, characterized in that the firing is in an oven in a non-oxidizing and non-reducing gas environment.

Description

The present invention relates to a process for the preparation of pigment particles, in particular of red pigment particles from mixed oxides containing manganese and zinc. Furthermore, the invention relates to red core-shell pigment particles of manganese and zinc containing mixed oxides and their use.

Pigments of manganese oxide-doped zinc oxides are known in the art. However, the art is of the opinion that the production of color pigment particles, in particular of red brilliant pigment particles of divalent manganese and divalent zinc-containing mixed oxides must necessarily take place in a reducing atmosphere.

The DE-PS 589 783 describes a method of preparing a blood red pigment from manganese oxide-doped zinc oxides comprising, in a first step, sulfates of divalent zinc and manganese in the following amounts: (a) ZnSO ₄ .7H ₂ O (43 g, 150 mmol) and (b ) MnSO ₄ * 4H ₂ O (11.2 g, 50 mmol) are first precipitated from aqueous solution, the carbonates, and this in a second step at a temperature of 700 ° C in a stream of 50 vol .-% carbon monoxide and 50 Vol .-% reduced carbon dioxide and then post-annealed in a third step in a de-oxygenated nitrogen stream at 900 ° C.

In the EP 0 484 444 In the comparative example number 2, a similar process is described for the preparation of an orange pigment from manganese oxide-doped zinc oxides, in which in a first step the sulphates of bivalent zinc and manganese are used in the following amounts: (a) ZnSO ₄ .7H ₂ O (431 , 31 g, 1.5 mol) and (b) MnSO ₄ .4H ₂ O (28.14 g, 126 mmol) are first precipitated from aqueous solution of the carbonates, washed in a second step, the precipitate with water sulfate-free, at 60 Dried for 2 hours and then ground and in a third step, the recovered precipitate is reduced at a temperature of 700 ° C in a stream of 50 vol .-% carbon monoxide and 50 vol .-% carbon dioxide for one hour and then in a fourth Step for one hour at 950 ° C tempered.

This dependency of the known methods on the use of carbon monoxide is extremely dangerous for the safety of the skilled personnel concerned in case of leakage of the equipment used, in which carbon monoxide leaks into the environment.

The two documents do not explicitly disclose which specific carbonates are suitable for the preparation of the pigment particles and, moreover, neither explicitly mention the use of (NH ₄ ) HCO ₃ or (NH ₄ ) ₂ CO ₃ as particularly suitable precipitants nor their technical effect Use on the particle size and the color homogeneity of the pigment particles produced.

The EP 0 484 444 discloses, in accordance with the invention, a process for the preparation of manganese oxide-doped zinc oxide pigments which comprises, in a first step, the oxide, hydroxide, carbonate and / or hydroxycarbonate of divalent zinc and of manganese in the presence of water with formic acid and / or oxalic acid for the conversion thereof in the processed into the corresponding formates or oxalates to a paste, in a second step, this paste dries, milled and calcined in a third step at temperatures of 700 to 1100 ° C in an inert gas atmosphere.

According to the patent application in question, it is not necessary to add reducing agents for the process just described since the formates or oxalates themselves have a reducing action and therefore there is no undesired oxidation of the divalent manganese oxides. As is known, the thermal decomposition of formates and oxalates also produces carbon monoxide.

From the prior art, another method for the preparation of doped with manganese oxide zinc oxides is known. For example, researchers have recently synthesized up to 17% manganese by manganese-based thermal zinc addition at temperatures of 850 ° C using NH ₄ Cl as a chemical transport reagent. ¹ As a result, they obtained a red pigment with the following Lab values: L * = 36.6, a * = 41.0, b * = 26.7.

However, even this alternative method should be dependent on a reducing agent, namely hydrogen gas, which is produced during the firing process. According to the researchers involved, the hydrogen gas that creates a reducing atmosphere is needed to preserve the bivalent manganese ions.

In our own laboratory experiments, it was found that this process is only of limited suitability to produce pigments, since during the firing process SiO ₂ ampoules are severely damaged. This was also reported by Saal et al. ¹ , possibly responsible substances for this include any gaseous decomposition products of NH ₄ Cl, metal chloride, metal oxide or even elemental metal vapors.

The object of the invention is to provide an alternative, improved process for the preparation of pigment particles of divalent manganese and divalent zinc-containing mixed oxides, which is particularly suitable for the production of the same on an industrial scale.

According to the invention, the object is achieved by a method comprising the features of claim 1. The subclaims relate to further advantageous and optionally inventive embodiments.

1. a. Bilden von Precursorpartikeln aus Mangan und Zink enthaltenden Mischcarbonaten, durch gemeinsame Fällung von Mangan- und Zinkcarbonaten mittels Zugabe eines Carbonat- und/oder Hydrogencarbonat-Salzes zu einer ersten wässrigen Lösung eines wasserlöslichen, zweiwertigen Zinksalzes und eines wasserlöslichen, zweiwertigen Mangansalzes in einem vorbestimmten Molverhältnis Zinksalz zu Mangansalz,
2. b. Isolieren der Precursorpartikel aus der ersten Lösung, Waschen und Trocknen derselben, und
3. c. Brennen der Precursorpartikel, um die Pigmentpartikel zu erhalten.

The present inventive method for the preparation of pigment particles from manganese and zinc-containing mixed oxides comprises the following steps:

1. a. Forming precursor particles of manganese and zinc-containing mixed carbonates, by coprecipitation of manganese and zinc carbonates by adding a carbonate and / or bicarbonate salt to a first aqueous solution of a water-soluble, divalent zinc salt and a water-soluble, divalent manganese salt in a predetermined molar ratio of zinc salt to manganese salt,
2. b. Isolating the precursor particles from the first solution, washing and drying them, and
3. c. Burning the precursor particles to obtain the pigment particles.

According to the invention, the firing takes place in an oven in a non-oxidizing and non-reducing gas environment.

Thus, the present invention takes a completely new path, as the present prejudice is known to experts, ie from Saal et al. ¹ and in particular from the EP0482444A1 based on the self-reducing acting precursor oxalates, is overcome.

In addition, the invention offers the advantage that you can work without the use of highly toxic carbon monoxide.

It is known that in the case of divalent manganese oxidation in the presence of zinc oxide, formation of hetaerolite (ZnMn ₂ O ₄ ), which is black, occurs. Of course, the hetaerolite itself adversely affects the desired color of the pigment particles, at least if colored, in particular red, brilliant pigment particles are to be obtained.

The inventors have observed in their experiments that red pigment particles can be obtained under selected firing conditions when ZnCl ₂ and MnCl _{2 are used} in a molar ratio of ZnCl ₂ to MnCl ₂ of 70:30 to 78:22.

In addition, they have observed that particularly brilliant red pigment particles can be obtained when ZnCl ₂ and MnCl _{2 are used} in a molar ratio of ZnCl ₂ to MnCl ₂ of 3.0.

Accordingly, according to a preferred embodiment of the process, ZnCl ₂ and MnCl _{2 are used} in a molar ratio ZnCl ₂ to MnCl ₂ of 70:30 to 78:22, preferably of 3.0.

According to a more general preferred embodiment of the process, a water-soluble divalent zinc salt and a water-soluble, divalent manganese salt in a molar ratio of zinc to manganese salt of from 70:30 to 78:22, preferably from 3.0 is used.

According to another preferred embodiment of the process are used as the zinc and manganese salt ZnCl ₂ and MnCl ₂ or ZnSO ₄ and MnSO ₄ , preferably ZnCl ₂ and MnCl ₂ .

In a further preferred embodiment of the process Mn (NO ₃ ) ₂ and Zn (NO ₃ ) ₂ are used as the zinc and manganese salt.

According to a further preferred variant of the method, the water-soluble carbonate and / or bicarbonate salt is selected from an alkali metal and / or a pseudoalkali (bi) carbonate, preferably from a group consisting of sodium (bi) carbonate, potassium (bi) carbonate , or ammonium (bi) carbonate, more preferably ammonium carbonate or ammonium bicarbonate.

According to a very preferred variant of the process, the ammonium bicarbonate is used as the water-soluble bicarbonate salt.

When the term "sodium (bi) carbonate" is used in this specification, it means Na ₂ CO ₃ and / or NaHCO ₃ . The same interpretation applies to "potassium (bi) carbonate" and "ammonium (bi) carbonate", ie by the term "potassium (bi) carbonate" is K ₂ CO ₃ and / or KHCO ₃ and by the term "ammonium (bi ) carbonate "is (NH ₄ ) ₂ CO ₃ and / or (NH ₄ ) HCO ₃ .

The inventors have now found that when using ammonium carbonate or ammonium bicarbonate as a precipitant color-homogeneous pigment particles are available. This is due to the fact that manganese and zinc carbonate are isomorphous and therefore homogeneously co-crystallizable in each molar ratio.

On the other hand, when Na ₂ CO _{3 was used} as the precipitating agent, pigment particles were obtained which in places have a similar or the same color as those pigment particles which were obtained when using ammonium carbonate or ammonium bicarbonate. However, these pigment particles were considered in terms of color inhomogeneous color, so that they have a different color, especially deviating hues in other places.

In this regard, a powder diffractogram was generated from the precursor precursor prepared according to the procedure of step a) of claim 1 and using Na ₂ CO ₃ as precipitant. The inventors were able to unambiguously assign the reflections observable in the relevant powder diffractogram to the sodium zinc carbonate of the formula Na ₂ Zn ₃ (CO ₃ ) ₄ .3H ₂ O.

It has thus been found that undesired Na ₂ Zn ₃ (CO ₃ ) ₄ * 3H ₂ O is precipitated when Na ₂ CO _{3 is used} in the precipitation of the precursor particles, which is the cause of the color inhomogeneity of the resulting pigment particles.

In a further experiment, the K ₂ CO _{3 was used} as a precipitant instead of the Na ₂ CO ₃ . Also in this experiment, color-inhomogeneous pigment particles were obtained.

Another disadvantage resulting from the use of Na ₂ CO ₃ is that the average particle size of the resulting pigment particles is greater than in the case of the use of ammonium carbonate or ammonium bicarbonate. The inventors agree that this result is due to the intrinsic properties of the Zn ₃ (CO _{3) 4} * 3 H ₂ O again released during the calcination of Na ₂ Na ₂ CO ₃ which melts at 851 ° C, and at firing temperatures of 1100 ° C acts as a flux, whereby the pigment particles partially clump.

Another disadvantage with the use of Na ₂ CO ₃ is also the lower particle uniformity of the pigment particles obtained than in the case of using NH ₄ HCO ₃ or (NH ₄ ) ₂ CO ₃ . This is also due to the low melting temperature of Na ₂ CO ₃ . Particularly disadvantageous in the case of such pigments obtained, for example, is their dispersibility in a carrier fluid of an ink owing to their inhomogeneous particle size distribution and thus particle uniformity. This also has a negative effect on the opacity, if such particles would be applied for example by means of roll-to-roll printing or screen printing on a surface to be printed in order to produce a printed image.

It has also surprisingly been found that the use of ammonium bicarbonate pigments are obtained with an average particle size, which are smaller than in the use of ammonium carbonate.

According to a preferred embodiment of the process according to the invention, the step of adding the water-soluble carbonate or bicarbonate salt takes place in the form of a second aqueous solution, the addition preferably being effected dropwise.

The step of adding may be done by stirring and cooling the first solution, preferably by cooling with an ice bath, and preferably cooling the first solution to a temperature below room temperature prior to the step of adding.

In a further preferred embodiment of the process according to the invention, the precursor particles obtained after step a) are aged in the first solution at a predetermined temperature, preferably between 0 to 30 ° C., for a predetermined period, preferably from 1 to 96 hours, before step b) is carried out.

1. a) ein einmaliges oder mehrmaliges Waschen der isolierten Precursorpartikel mit Wasser, vorzugsweise deionisiertem Wasser, der darauf gerichtet ist, wasserlösliche Salze zu entfernen,
2. b) vorzugsweise ein einmaliges oder mehrmaliges Waschen der aus dem Waschschritt a) erhaltenen Precursorpartikel mit Aceton.

According to a further preferred embodiment of the method, the step of washing comprises the following steps:

1. a) washing the isolated precursor particles once or more with water, preferably with deionized water, aimed at removing water-soluble salts,
2. b) preferably a single or multiple washing of the precursor particles obtained from the washing step a) with acetone.

The use of acetone has the advantage that the majority of the water in the precipitate is removed, whereby a faster drying is made possible and beyond the imparting of the Precursorpartikel can be at least partially reduced.

The isolated precursor particles can be washed in the washing step a) with an ammonium sulfate solution instead of water, preferably with a 0.05% ammonium sulfate solution, followed by a further washing step a1) with deionized water.

The step of drying in step b) of the process according to the invention can be carried out, for example, at temperatures between 60 and 120.degree. C., preferably between 80 and 100.degree.

According to a preferred embodiment of the process according to the invention, the firing is carried out in at least two stages, optionally in the first stage, heating and holding at temperatures in a range of 350 to less than 850 ° C to the precursor at least partially, preferably completely in decarboxylated manganese and zinc-containing mixed oxide precursor particles and CO ₂ , and in the second stage, comprising heating the mixed oxide precursor particles obtained from the first stage and maintaining them at temperatures in the range of 850 to 1200 ° C to obtain the pigment particles.

According to a preferred embodiment of the method according to the invention, the gas environment is formed without the addition of an oxidizing and / or reducing material.

According to a particularly preferred embodiment of the method according to the invention, the gas environment is formed by adding a non-oxidizing and non-reducing protective gas, preferably by means of a protective gas flow.

As the protective gases, noble gases such as argon or inert gases such as nitrogen are preferably used during firing.

In the second firing step, interdiffusion reactions occur in which Mn atoms and Zn atoms interdiffuse in the present mixed crystal. If now red pigment particles are to be produced, the expert in carrying out the second firing step must always make sure that the firing time at a selected temperature is not too long, since otherwise pigment particles having a brownish hue are obtained (results corroborated by Saal et al ¹ ).

According to a preferred variant of the method, the firing in the second stage takes place at temperatures of 850 to 1200 ° C for a period of 1 to 360 minutes, preferably at temperatures of 950 to 1150 ° C for a period of 1 to 30 minutes, more preferably at temperatures of 1050 to 1100 ° C for a period of 1 to 10 min.

According to a particularly preferred variant of the process, the firing in the second stage takes place at temperatures of 1000 ° C. for a period of 30 minutes, preferably at a temperature of 1050 ° C. for a period of 15 minutes and particularly preferably at a temperature of 1100 ° C for a duration of 1 min.

According to a preferred variant of the method, the firing in the first stage takes place at temperatures in a range of greater than 350 and less than 850 ° C., preferably in a range of greater than 500 and less than 850 ° C., and more preferably in a range of greater than 500 and smaller 650 ° C.

The heating may be carried out in the first and / or second stage at a heating rate of 3 to 25 ° C / min, preferably 5 to 15 ° C / min, and more preferably at a heating rate of 10 to 15 ° C / min.

It has also surprisingly been found in selected experiments that firing is at least temporarily under vacuum at a pressure and at conditions effective to remove zinc (II) oxide from an outer layer of the mixed oxide precursor particles and / or the pigment particles , Pigment particles can be obtained, each having a molar ratio of divalent manganese with respect to the divalent zinc in the outer surface layer and thus in the shell of a pigment particle, which is higher than in the rest and thus in the core of the corresponding pigment particle.

Accordingly, according to a particularly preferred embodiment of the method, the firing takes place at least temporarily under vacuum at a pressure and under conditions effective to remove zinc (II) oxide from an outer layer of the mixed oxide precursor particles and / or the pigment particles, and which are chosen such that pigment particles are obtained, each having a molar fraction of divalent manganese with respect to the molar fraction of bivalent zinc in an outer surface layer and thus in the shell of a pigment particle which is higher than in the rest and thus in the core of corresponding pigment particle.

Thus, mixed oxides containing manganese and zinc pigment particles are obtainable by such a method which has a molar ratio of divalent manganese with respect to the molar ratio of the divalent zinc in an outer surface layer and thus in a shell of the pigment particles higher than the rest and thus at the core of the pigment particles.

These pigment particles have a difference between the refractive indices of the core and the cladding. This method thus offers a simple way to control the color of the pigment particles specifically, without the initial amount of MnCl ₂ and ZnCl ₂ or the more generally claimed water-soluble bivalent zinc and Manganese salts for a desired color must be tailored.

Preferably, pigment particles are obtainable by this method, which have a positive radial gradient of the molar fraction of divalent manganese with respect to the molar fraction of divalent zinc in the outer layer and thus in the shell of the pigment particles.

When referred to in this description of a positive radial gradient, this refers to an increasing concentration with increasing radius of the pigment particles.

The inventors have observed in selected experiments that if the burning of the precursor particles is carried out at a pressure of less than 300 mbar, the resulting pigment particles often appear as red with green dots. In these experiments, ZnCl ₂ and MnCl _{2 were used} in a molar ratio of ZnCl ₂ and MnCl ₂ of 3.0. In the investigations carried out, it has been found that the green dots are manganese (II) oxide.

Although the inventors can not be limited to a single explanation or theory, it is believed that removal of the zinc (II) oxide under the conditions described above may be by sublimation. The formation of manganese (II) oxide (manganositol) in the above-mentioned experiments only allows the conclusion that a certain amount of zinc (II) oxide has been removed from the pigment particles.

According to a particularly preferred embodiment of the method, therefore, the firing takes place at least temporarily at a pressure in a range between 300 and 700 mbar and preferably at temperatures in a range of 600 ° C and 1200 ° C.

According to a very particularly preferred embodiment of the method, the thickness of the shell of the pigment particles and the molar fraction of divalent manganese with respect to the molar fraction of divalent zinc in the shell of the pigment particles by an appropriate choice of pressure, the firing temperature and their exposure time to the mixed oxide Precursor particles and / or pigment particles.

The vacuum is applied either in the first and / or second stage, preferably in the second stage.

In a preferred embodiment of the method according to the invention, the firing takes place in a rotary kiln, which is preferably operated under constant rotation.

The following experimental examples are intended to illustrate in more detail the performance of particularly preferred processes according to the invention for the preparation of preferred pigments having a brilliant red hue, without, however, being limited thereto.

Trial 1:

Formation of Precursor Particles:

MnCl ₂ * 4H ₂ O (49.5 g, 250 mmol) and ZnCl ₂ (102.2 g, 750 mmol) were dissolved in 250 ml of deionized water. To this first solution was slowly added (NH ₄ ) ₂ CO ₃ (96.1 g, 1000 mmol), predissolved in 500 ml of deionized water, with stirring. The precipitate formed was separated by filtration and washed 3 times with 250 ml of deionized water and 2 times with 250 ml of acetone and dried overnight in a drying oven at a temperature of 100 ° C.

Precursor particles were synthesized from manganese and zinc containing mixed carbonates.

II. Formation of the pigment particles:

9.6 g of the manganese and zinc precursor particles containing mixed manganese precursors were placed in a RCA (Recrystallised Alumina) RCA tube and in a first firing step using an inert gas stream of nitrogen at a heating rate of 10 ° C / min heated to a temperature of 500 ° C and held at this temperature for a period of 15 min to convert the precursor particles into the corresponding manganese and zinc containing obtained mixed oxide precursor particles and CO ₂ . Subsequently, the resulting mixed oxide precursor particles were heated in a second firing step under a pressure of 500 mbar at a marriage of 10 ° C / min to a temperature of 1100 ° C and held at this temperature for a period of 1 min to the pigment particles receive. Finally, the obtained pigment particles were cooled to room temperature.

Brilliant red pigment particles with a mean particle size (d 0.5) of 10 μm and Lab values of L * = 32, a * = 40, b * = 26 were obtained.

Trial 2:

• MnCl₂ (31,5 g, 250 mmol) und ZnCl₂ (102,2 g, 750 mmol) wurden in 2 Liter deionisiertem Wasser gelöst. Zu dieser ersten Lösung wurde (NH₄)HCO₃ (158,1 g, 2000 mmol), vorgelöst in 800 ml deionisiertem Wasser, mit einer Geschwindigkeit von 2 Tropfen/sec unter Rührung der ersten Lösung zugetropft. Die resultierende Reaktionsmischung wurde 2 Tage lang unter Rühren altern gelassen, der Niederschlag durch Filtration abgetrennt und 3-mal mit je 400 ml einer 0,05 Gew% (NH₄)₂SO₄-Lösung und anschließend mit 400 ml deionisiertem Wasser gewaschen, das gewaschene Filtrat in 1 Liter Aceton dispergiert und filtriert und anschließend für 1 Tag in einem Trockenschrank bei 80°C getrocknet.

I. Formation of Precursor Particles: This specification is based on a method adapted from the inventors of the present application Saito et al. ² , in which manganese and zinc chloride were used instead of yttrium nitrate:

• MnCl ₂ (31.5 g, 250 mmol) and ZnCl ₂ (102.2 g, 750 mmol) were dissolved in 2 liters of deionized water. To this first solution was added (NH ₄ ) HCO ₃ (158.1 g, 2000 mmol) predissolved in 800 ml of deionized water at a rate of 2 drops / sec while stirring the first solution. The resulting reaction mixture was allowed to age for 2 days with stirring, the precipitate separated by filtration and washed 3 times with 400 ml each of a 0.05 wt% (NH ₄ ) ₂ SO ₄ solution and then with 400 ml of deionized water washed filtrate in 1 liter of acetone and filtered and then dried for 1 day in a drying oven at 80 ° C.

Precursor particles were synthesized from manganese and zinc containing mixed carbonates.

II. Formation of the pigment particles:

12.5 g of the above-obtained precursor particles of manganese and zinc-containing mixed carbonates were placed in a corundum boat in a vacuum tube furnace and heated to a temperature of 500 ° C in a first firing step using an inert gas stream of nitrogen at a heating rate of 10 ° C / min and held at that temperature for a period of 20 minutes to convert the precursor particles to the corresponding manganese and zinc containing mixed oxide precursor particles and CO ₂ . Subsequently, the mixed oxide precursor particles contained were heated in a second firing step under a pressure of 500 mbar at a marriage of 10 ° C / min to a temperature of 1100 ° C and held at this temperature for a period of 1 min to the pigment particles to obtain the manganese and zinc-containing mixed oxides. Finally, the obtained pigment particles were cooled to room temperature.

Brilliant red pigment particles with an average particle size d (0.5) of about 8.5 μm and Lab values of L * = 35, a * = 40, b * = 26 were obtained.

References:

1. 1. Saal, H., Binnewies, M., Schrader, M., Börger, A., Becker, K.-D., Tikhomirov, Viatcheslav A. and Jug, K. (2009), Unusual Optical Properties of Mn-doped ZnO : The Search for a New Red Pigment-A Combined Experimental and Theoretical Study. Chem. Eur. J., 15: 6408-6414. doi: 10.1002 / chem.200802667
2. Second Saito, N., Matsuda, S.-I. and Ikegami, T. (1998), Fabrication of Transparent Yttria Ceramics at Low Temperature Using Carbonate-Derived Powder. Journal of the American Ceramic Society, 81: 2023-2028. doi: 10.1111 / j.1151-2916.1998.tb02583 .x

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 589783 [0003]
• EP 0484444 [0004, 0007]
• EP 0482444 A1 [0016]

Cited non-patent literature

• Saal, H., Binnewies, M., Schrader, M., Börger, A., Becker, K.-D., Tikhomirov, Viatcheslav A. and Jug, K. (2009), Unusual Optical Properties of Mn-doped ZnO : The Search for a New Red Pigment-A Combined Experimental and Theoretical Study. Chem. Eur. J., 15: 6408-6414. doi: 10.1002 / chem.200802667 [0072]
• Saito, N., Matsuda, S.-I. and Ikegami, T. (1998), Fabrication of Transparent Yttria Ceramics at Low Temperature Using Carbonate-Derived Powder. Journal of the American Ceramic Society, 81: 2023-2028. doi: 10.1111 / j.1151-2916.1998.tb02583 [0072]

Claims (23)

Process for the preparation of pigment particles from mixed oxides containing manganese and zinc, comprising the following steps: a. Forming precursor particles of manganese and zinc-containing mixed carbonates, by coprecipitation of manganese and zinc carbonates by adding a carbonate and / or bicarbonate salt to a first aqueous solution of a water-soluble, divalent zinc salt and a water-soluble, divalent manganese salt in a predetermined molar ratio of zinc salt to manganese salt, b. Isolating the precursor particles from the first solution, washing and drying them, and c. Firing the precursor particles to obtain the pigment particles, characterized in that the firing is in an oven in a non-oxidizing and non-reducing gas environment. Method according to Claim 1 characterized in that the gas environment is formed without addition of an oxidizing and / or reducing material. Method according to Claim 1 or 2 characterized in that the gas environment is formed by adding a non-oxidizing and non-reducing protective gas, preferably by means of a protective gas stream. Method according to at least one of the preceding claims, characterized in that ZnCl ₂ and MnCl ₂ or ZnSO ₄ and MnSO ₄ , preferably ZnCl ₂ and MnCl ₂ are used as the zinc and manganese salt. Process according to at least one of the preceding claims for the preparation of red pigment particles, characterized in that the zinc and manganese salt in the molar ratio zinc salt to manganese salt is used from 71:29 to 78:22, preferably from 3.0. Method according to at least one of the preceding claims, characterized in that the water-soluble carbonate and / or bicarbonate salt is selected from at least one alkali and / or at least one pseudoalkali (bi) carbonate, preferably from a group consisting of sodium (bi) carbonate Potassium (bi) carbonate or ammonium (bi) carbonate, more preferably ammonium carbonate or ammonium bicarbonate, and most preferably ammonium bicarbonate. Method according to at least one of the preceding claims, characterized in that the step of adding the water-soluble carbonate or bicarbonate salt takes place in the form of a second aqueous solution, wherein the addition is preferably carried out dropwise. Method according to at least one of the preceding claims, characterized in that the step of adding is carried out with stirring and cooling of the first solution, wherein the cooling is preferably carried out by means of ice bath, and preferably wherein the first solution is cooled to a temperature below room temperature prior to the step of adding , Method according to at least one of the preceding claims, characterized in that the precursor particles obtained after step a) are allowed to age in the first solution at a predetermined temperature, preferably between 0 to 30 ° C, for a predetermined period, preferably from 1 to 96 hours before step b) is performed. Method according to at least one of the preceding claims, characterized in that the step of washing comprises: a. washing the isolated precursor particles once or more with water, preferably deionized water, which is directed to remove water-soluble salts, b. preferably a single or multiple washing of the precursor particles obtained from the washing step a) with acetone. Method according to Claim 10 in that the isolated precursor particles are washed in the washing step a) with an ammonium sulfate solution instead of water, preferably with a 0.05% ammonium sulfate solution, followed by a further washing step a1) with deionized water. Method according to at least one of the preceding claims, characterized in that the firing is carried out in at least two stages, comprising optionally heating in the first stage and holding at temperatures in a range from 350 to less than 850 ° C to at least partially remove the precursor particles, preferably converting fully decarboxylated manganese and zinc-containing mixed oxide precursor particles and CO ₂ , and in the second step, heating the mixed oxide precursor particles obtained from the first step and maintaining them at temperatures in the range of 850 to 1200 ° C to obtain the To obtain pigment particles. Method according to Claim 12 characterized in that the firing in the second stage at temperatures of 850 to 1200 ° C for a period of 1 to 360 minutes, preferably at Temperatures of 950 to 1150 ° C for a period of 1 to 30 min and more preferably at temperatures of 1050 to 1100 ° C for a period of 1 to 10 min, takes place. Method according to Claim 13 characterized in that the firing in the second stage is carried out at a temperature of 1000 ° C for a period of 30 minutes, preferably at a temperature of 1050 ° C for a period of 15 minutes and more preferably at a temperature of 1100 ° C for a Duration of 1 min. Method according to at least one of Claims 12 to 14 characterized in that the firing in the first stage at temperatures in a range of greater than 350 and less than 850 ° C, preferably in a range of greater than 500 and less than 850 ° C, more preferably in a range greater than 500 and less than 650 ° C. he follows. Method according to at least one of Claims 12 to 15 characterized in that the heating in the first and / or second stage at a heating rate of 3 to 25 ° C / min, preferably from 5 to 15 ° C / min and more preferably at a heating rate of 10 to 15 ° C / min , Method according to at least one of the preceding claims, characterized in that the firing takes place at least temporarily under vacuum at a pressure and under conditions which are effective for removing zinc (II) oxide from an outer layer of the mixed oxide precursor particles and / or pigment particles and the conditions are preferably selected such that pigment particles are obtained whose respective molar fraction of divalent manganese is higher in relation to the molar fraction of divalent zinc in an outer surface layer and thus in a shell of a pigment particle than in the remainder and thus in the core the corresponding pigment particle. Method according to Claim 17 characterized in that the burning takes place at least temporarily at a pressure in a range between 300 and 700 mbar and at temperatures in a range of 600 ° C and 1200 ° C. Method according to Claim 17 or 18 characterized in that the thickness of the shell of the pigment particles and the molar fraction of divalent manganese with respect to the molar fraction of divalent zinc in the shell of the pigment particles by an appropriate choice of the pressure, the firing temperature and their exposure time to the mixed oxide precursor particles and / or Pigment particle is determined. Method according to at least one of Claims 17 to 19 characterized in that the vacuum is applied selectively in the first and / or second stage, preferably in the second stage. Red pigment particles of mixed oxides containing manganese and zinc obtainable by a process according to at least one of Claims 17 to 20 based on Claim 5 which have a molar proportion of divalent manganese in an outer surface layer and thus in a shell of the pigment particles, which is higher than in the rest and thus in the core of the pigment particles. Red pigment particles after Claim 21 characterized in that the pigment particles have a positive radial gradient of the divalent manganese with respect to the molar fraction of divalent zinc in the outer layer and thus in the shell of the pigment particles. Use of the pigment particles according to at least one of Claims 21 or 22 for coloring glass frits, lacquers, printing inks, inks, plastics, glasses or ceramic products.