DE4119668A1 - Yellow bismuth vanadate pigment - is produced from bismuth and vanadium oxide in nitric acid suspension and used for pigmenting lacquer and plastics - Google Patents

Abstract

Prodn. of yellow BiVO4 pigment (I) involves reaction of a mixt. contg. Bi2O3 and V2O5 in HNO3 suspension at under 100, pref. 20-50 deg.C. Reaction is carried out at solids contents up to 70 (wt.)% and HNO3 concns. up to 65%, at a Bi:V molar ratio of 1:(1.00-0.60), pref. 1:(0.95-0.80). After (I) formation, HNO3 is removed by washing and/or evapn. USE/ADVANTAGE - (I) is useful for pigmenting lacquers and plastics. It is also useful in other paints. The (I) obtd. is bright yellow and or extremely high colouristic quality. At 10% pigment vol. concn. (PVC) in alkyd lacquer, the colour values (DIN 6174) are A = 0 to -10, B = 80 to 90, C = 80 to 90 and L = 85 to 90.

Description

The present invention relates to a method for producing BiVO₄ yellow pigments as well as their use.

Bismuth vanadate, BiVO₄, occurs as an alternative product for cadmium, lead and Chromium (VI) -containing inorganic pigments have been increasing in the past few years Foreground.

The technical manufacturing processes for BiVO₄ yellow pigments can be divided into two groups:
In the gel precipitation method, amorphous bismuth vanadates are precipitated from solutions of bismuth (III) salts and alkali metal vanadates and these are calcined after separation from the mother liquor (DE-C 27 27 863, DE-A 27 27 864).

The solid method uses bismuth and vanadium-containing starting substances, preferably oxides, hydroxides, carbonates and nitrates, mechanically in the solid state well mixed and then by annealing at higher temperatures to BiVO₄ implemented (DE-C 27 27 865).

For the technical production of strong and opaque yellow pigments in the solid process for annealing, the presence of nitrate-containing substances proven necessary (DE-C 33 15 850, 33 15 851). But this too In contrast to the gel precipitation method, the measure leads to less brilliant, greenish, slightly dirty pigments.

The object of this invention is to provide a method which does not have the disadvantages described.

The present invention overcomes these disadvantages and leads to coloristic extraordinarily high-quality color bodies.

Surprisingly, it has been shown that one is particularly brilliant and strong yellow pigments are obtained when the reaction of Bi₂O₃- and V₂O₅- containing starting mixtures in strongly nitric acid suspensions Performs temperatures below 100 ° C.

The invention thus relates to a process for the preparation of BiVO₄ yellow pigments, where Bi₂O₃- and V₂O₅-containing starting mixtures in nitric acid Suspension at temperatures <100 ° C, preferably between 20 and 50 ° C, implemented will.

Depending on the temperature and particle size of the starting substances, the Response from a few hours to several days. After pigment formation is complete the remaining nitric acid is removed. This can be done by heating the Reaction mixture to 120 to 160 ° C or by washing with H₂O. The nitrate-free pigment is then further processed according to the known methods processed (grinding, drying, post-treatment, deagglomeration).

Particularly good results are achieved if the implementation of the bismut and vanadium-containing solid mixtures in nitric acid medium with solids contents up to 70 wt .-% and nitric acid concentrations up to 65 wt .-%.

In syntheses at the limits of the concentration range according to the invention BiVO₄ also in small quantities in the form of a second structure type, namely zirconium silicate - ZrSiO₄- occur.  

The preferred bismuth component for the present process is bismuth nitrate, Bi (NO₃) ₃, or bismuth oxide nitrate, BiONO₃, but others can also in HNO₃ sufficiently soluble bismuth compounds such as bismuth oxides or carbonates Find use. Bismuth metal can also be used if it is used as a powder there are sufficiently small particles.

Vanadium pentoxide, V₂O₅ is preferably in powder form as the vanadium component Use. Because technical V₂O₅ with significantly different particle sizes is offered, it is advantageous when changing the type, the necessary response time new to determine.

The preparation of the starting mixture from the bismuth and vanadium components is preferably carried out by wet grinding. The raw materials are so much H₂O added that suspensions of a maximum of 70 wt .-% solids result. Will the Bismuth component specified as bismuth oxide nitrate or bismuth nitrate is not used additional nitric acid is required because of the implementation

2 BiONO₃ + V₂O₅ + H₂O → 2 BiVO₄ + 2 HNO₃

sufficient amounts of HNO₃ are formed. For nitrate-free raw materials must be added so much nitric acid that at least 1 mol of NO₃ per 1 mol of Bi is present and the concentration of HNO₃ in the batch - after the reaction - reached a maximum of 65% by weight.

The starting substances are not specified in the molar ratio in BiVO V (Bi: V = 1: 1). Rather, it has been shown that a small deficit of vanadium leads to particularly strong and brilliant yellow pigments. The range from Bi _1.00 V _0.98 to Bi _1.00 V _0.60 is preferred for the molar Bi: V ratio, molar ratios corresponding to the composition of Bi _1.00 V _0.95 to Bi _1.00 V _{0.80 being} very particularly preferred.

The nitric acid-containing starting mixtures are initially at room temperature, but at most at 100 ° C, brought to reaction. For this manufacturing step  times of 10 to 72 hours have proven to be favorable. Because the reaction mixtures in the course of the implementation of a dirty brown green after a brilliant, strong yellow color, the end of the reaction is no problem noticeable. The nitric acid is removed in a second reaction step. That can by increasing the temperature to about 150 ° C, whereby to complete Removal of nitric acid is generally sufficient for 2 to 4 hours.

The nitric acid can also in the course of the subsequent workup, for. B. in a wet grinding step, be removed by washing.

After formation of the BiVO₄ pigment, preference is given to nitric acid Wash out or smoke removed.

Wet grinding takes place in ball or sand mills. The subsequent washing step must be adapted to the respective application and opens up the possibility for the aftertreatment of the pigments, e.g. B. with deflocculants, or the Application of protective layers to increase the thermal resistance in Plastics.

For applications where such measures are not necessary, the Grinding also dry, e.g. B. in mortar, pen or cross beater mills.

Since the synthesis according to the invention, in contrast to the method according to the prior art technology takes place at a very low temperature, is obtained in the reaction products Particles for use in pigments without further crushing can be used. That is why the described grinding steps serve homogenization and deagglomeration rather than crushing Reaction products.

The bismuth vanadates produced according to the invention are found as bright yellow Substances mainly in the pigment industry in paints and others Paint or for coloring plastics use.  

The bismuth vanadates produced by the process according to the invention have a structure very similar to the Scheelit (CaWO₄), whereby in most cases the tetragonal lattice of the CaWO₄ appears more or less distorted monoclinic, what about a split of characteristic lines in the X-ray powder diagram can be seen.

The coloristic values of the pigments produced according to the invention depend on predetermined Bi: V ratio and depending on the particle size present, however, the limits of the values obtained can be measured in the color field (measured in Alkydal®-F48-Lack / Purton (Alkyldal® = alkyd resin from Bayer AG) with 10% Specify PVC according to DIN 6174) as follows:

a * = 0 to -10
b * = 80 to 90

C * = 80 to 90
L * = 85 to 90

This invention also relates to the use of the invention manufactured BiVO₄ yellow pigments for coloring paints and plastics.

In the following the invention will be explained by way of example without any Restriction can be seen.  

example 1

In a 1 liter ball mill 2040.5 g of BiONO₃ and 541.5 g of V₂O₅ with 1100 g Grind H₂O wet for one hour. The suspension with the molar ratio Bi: V = 1: 0.85 and a solids content of 70% by weight is on an enamel sheet poured and left for 72 hours at room temperature. In these times the color changes from green-brown to yellow. To remove the formed Nitric acid heats the reaction product for a total of 3 hours, starting with a temperature of 90 ° C and gradually increasing to 160 ° C.

The nitric acid-free preparation is then placed in one for 15 minutes Ball mill wet milled, washed out, dried and deagglomerated.

Has an average sample of the brilliant BiVO₄ yellow pigment obtained - Under the above-mentioned measurement conditions in Alkydal® lacquer (Alkydal® = alkyd resin from Bayer AG) - the following Color values:

L * = 86.6
C * = 88.4

a * = -6.6
b * = 88.2

Example 2

In a 1 liter ball mill, 583 g of BiONO₃ together with 154 g of V₂O₅ and Grind 350 g of H₂O wet for 30 minutes. The suspension with the molar Ratio Bi: V = 1: 0.85 is initially 72 hours at room temperature kept. The resulting brilliant yellow reaction product is then heated to 90 to 150 ° C (a total of 3 hours) to the resulting To remove nitric acid. Finally, the pigment is in a mortar grinder ground dry.

A brilliant, bright yellow structure with a monoclinic structure is obtained (distorted Scheelite grating) without secondary components with the following grating constants:

a _o = 5.18₃ Å
b _o = 11.70₁ Å
c _o = 5.10₁ Å

β = 90.315 °

The color values are:

L * = 86.6
C * = 89.6

a * = -6.2
b * = 89.4

Examples 3 to 10

The following examples were carried out completely analogously to Example 2, however different molar Bi: V ratios in given the suspensions. The for the investigated molar ratios between Bi: V = 1: 1.00 and Bi: V = 1: 0.50 gram quantities are in Table 1 compiled.  

Table 1

Gram amounts and molar ratios of Examples 3 to 10

After reaction at room temperature, removal of the HNO₃ at 150 ° C and grinding Analogously to Example 2, yellow pigments were combined with those listed in Table 2 Get color values. Optimal C * and b * values were then at predetermined molar ratios between Bi: V = 1: 0.95 and Bi: V = 1: 0.80 found.  

Table 2

Color values and results of X-ray powder diffractometry Examples 3 to 10

The main phase in all pigments is a more or less mono clin-distorted Scheelite lattice. In addition, the pigments occur with high Vanadium deficit as 2nd crystalline phase also small amounts of zircon silicate structure - ZrSiO₄ - on. The results of X-ray powder diffractometry are included in Table 2.

Example 11

In a ball mill, 41.8 g of bismuth metal powder together with 17.3 g Grind V₂O₅ and 18 ml H₂O for 30 minutes. The suspension obtained is with Nitric acid (28 ml 65% by weight HNO₃, density = 1.39 g / ml, in 20 ml H₂O) transferred. The development of nitrous gases that occurs after about Completed 10 minutes.

The reaction mixture is then kept at room temperature for 24 hours, the implementation of BiVO₄ is in full process. The removal of the Nitric acid happens - as already described several times - by heating the Substance to 90 to 160 ° C (evenly increasing temperature, a total of 3 Hours). The reaction product is finally dried in a cross beater mill ground up.

A bright yellow pigment with a monoclinic crystal lattice (distorted Scheelite structure).

The color values of the pigment are:

L * = 86.6
C * = 87.6

a * = -9.7
b * = 87.1

Example 12

In a porcelain ball mill, a mixture of 46.6 g Bi₂O₃ and 17.3 g V₂O₅ with a solution of 14 ml HNO₃ (65 wt .-%) in 14 ml H₂O and 30th Minutes. The phase obtained is kept at 20 ° C. for 72 hours. How in the previous examples, the nitric acid is heated to 90 to 150 ° C (a total of 3 hours) and the reaction product obtained then ground dry in a mortar mill.

A bright yellow pigment powder is obtained with the following color values:

L * = 90.4
C * = 84.9

a * = -15.9
b * = 83.4

The X-ray powder diffractogram shows the monoclinic BiVO₄ structure without Foreign lines as in Example 11.

Example 13

In the present example, the bismuth nitrate is converted to BiVO₄ liberated nitric acid not by heating, but by washing out with H₂O removed. 58.3 g of BiONO₃, 15.5 g of V₂O₅ and 32 ml of H₂O in one Porcelain ball mill wet grinding for 15 minutes. The resulting suspension remains stand for reaction for 48 hours at room temperature. The brilliant yellow obtained Paste is washed on a Nutsche with distilled H₂O until in Filtrate no longer shows nitrate. The filter cake is at 120 ° C in Drying cabinet dried and then dry in a cross beater mill ground.

The yellow pigment obtained has the following color values:

L * = 86.3
C * = 88.2

a * = -5.9
b * = 88.0

The following counterexamples show that one is much worse coloristic values are obtained if the nitrate-containing reaction mixtures are not according to the invention at room temperature, but the pigment formation after the state of the art by annealing at a higher temperature.

Comparative example

As in Example 11, 41.8 g of bismuth metal powder and 17.3 g V₂O₅ in 18 ml H₂O wet grinding for 30 minutes. After moving the Grist with 28 ml of HNO₃ (65% by weight) in 20 ml of H₂O releases nitrous gases, which is finished after about 10 minutes. The substance is thereupon Dried in a drying cabinet at 125 ° C and ground in a cross beater mill. The powder obtained is calcined at 500 ° C. for 6 hours and then again dry ground.

A dirty-looking, greenish yellow pigment is obtained with the following Color values:

L * = 73.6
C * = 71.2

a * = 2.3
b * = 71.1

Comparative Example 2

In a ball mill are as in Example 12 46.6 g Bi₂O₃ and 17.3 g V₂O₅ with Nitric acid (14 ml 65% HNO₃ in 25 ml H₂O) wet milled for 30 minutes. The suspension obtained is dried in a drying cabinet at 125 ° C. and in a cross beater mill dry milled.

According to the state of the art, pigment formation occurs at 500 ° C within 6 Hours.  

The reaction product is ground dry again, a dirty yellow Pigment with the following color values results:

L * = 75.45
C * = 72.1

a * = 0.79
b * = 72.1

Comparative Example 3

From 58.3 g BiONO₃, 17.3 g V₂O₅ and 32 ml H₂O is in a porcelain ball mill prepared by grinding for 15 minutes, which is then at 125 ° C in Drying cabinet is drained for 6 hours. This intermediate is then in crushed in a cross beater mill and heated to 500 ° C for 6 hours. That after The pigment obtained in the prior art gives after repeated grinding following color values:

L * = 73.7
C * = 68.7

a * = 1.0
b * = 68.7

Claims (5)

1. A process for the preparation of BiVO₄ yellow pigments, characterized in that Bi₂O₃- and V₂O₅-containing starting mixtures in nitric acid suspension at temperatures <100 ° C, preferably between 20 ° C and 50 ° C, are implemented. 2. The method according to claim 1, characterized in that after formation of the BiVO₄ pigment by washing out or by nitric acid Smoking is removed. 3. The method according to any one of claims 1 or 2, characterized in that that the reaction at solids contents up to 70 wt .-% and at Nitric acid concentrations up to 65 wt .-% is carried out. 4. The method according to one or more of claims 1 to 3, characterized characterized in that the molar Bi: V ratios of the reaction mixtures between 1: 1.00 and 1: 0.60, preferably between 1: 0.95 and 1: 0.80. 5. Use of the produced according to one or more of claims 1 to 4 BiVO₄ yellow pigments for coloring paints and plastics.