DE4235946A1 - Process for the production of pure iron oxide direct red pigments and their use - Google Patents

Description

The present invention relates to a method for Production of pure iron oxide direct red pigments Precipitation of iron (II) salts with alkali solution and oxida tion with oxygen-containing gases, addition of iron (II) saline solution and metallic iron or of iron (II) salt solution and alkali solution to the germ thus obtained suspension and oxidation with oxygen-containing gases until the desired color and their color is reached Use.

There are four processes for producing red iron oxide pigments known (T.C. Patton, Pigment Handbook, Vol. 1, New York 1988, p. 288). One of them is direct Precipitation of red iron oxides as described in US-A 2,716,595 is described. This is an iron (II) salt solution and an alkali solution in approximately equivalent amounts mixed and by the iron (II) hydroxide obtained or carbonate suspension air passed through. The so  resulting iron (III) oxide hydroxide suspension in the presence of iron (II) salt with the addition of metal iron with heating and oxidizing with acid gases containing substances built up to the red pigment.

From DE-B 10 84 405 it is known that red pigments only can be made from red germ suspensions. Pure red iron oxide seed suspensions are after the US-A-3 946 103 through the use of seed modifiers produced.

The pigments produced by this process have compared to those by calcination of yellow and black Pigments made of iron oxides due to their Softness improved properties in terms of Dispersibility, gloss and flocculation behavior, especially in applications in paint systems. The Color purity of by direct precipitation according to the US-A 3 946 103 iron oxide red pigments produced are sufficient but in paint applications not to that of Calzi nation of black and yellow iron oxides obtained Red pigments.

The object of the present invention is therefore a Process for the preparation of iron oxide red pigments for To provide which the above described Does not have disadvantages.

Surprisingly, such a method has now been found, whereby first a black magnetite seed suspension (Fe ₃ O ₄ ) is produced and this is carried out after a ripening step and after addition of iron (II) salt solution and metallic iron or after addition of iron (II) salt solution and alkali solution Heating and oxidizing with oxygen-containing gases is converted into a red pigment that has a high color purity.

The germ suspension consists of fine-particle megnetite. The specific surface area is larger than 60 m ² / g (nitrogen adsorption according to BET, single point method - DIN 66131), the average particle size is smaller than 0.05 µm (electron micrograph).

The present invention thus relates to a process for the preparation of pure iron oxide direct red pigments by precipitation of iron (II) salts with alkali solution and oxidation with oxygen-containing gases, addition of iron (II) salt solution and metallic iron or of iron (II) salt solution and alkali solution to the thus obtained germ suspension and oxidation with oxygen-containing gases until the desired color is reached, a black magnetite germ suspension with a specific surface area <60 m ² / g and an average particle size <0.05 µm being used to build up the pigment.

That this process leads to color-pure iron oxide red pigments, is particularly surprising because it is known from US-A-5 076 848 that the occurrence of magnetite in the manufacture of iron oxide yellow and red pigments lead to significant losses in color purity leads.  

In the method according to the invention, it is both possible the germ suspension in the suspension by suitable Manufacture conditions yourself as well as separately put germs to use.

A preferred embodiment of the inventive Ver driving is that to produce the germs pension

• a) an aqueous iron (II) sulfate solution with a Concentration from 10 to 80 g / l, preferably 20 to 40 g / l, submitted,
• b) with 0.8 to 1.5, preferably 0.9 to 1.1 equiva lenten an alkaline precipitant and
• c) for oxidation with air in an amount of 20 to 300 l per hour and liter of suspension intensive is fumigated.

To prepare the iron (II) sulfate solution can be iron (II) salts from steel pickling plants are particularly preferred and / or titanium dioxide production can be used.

The temperature during nucleation is preferably 30 up to 80 ° C, particularly preferably 30 to 50 ° C.

A suspension of iron (II) is added by adding 0.8 to 1.5 equivalents, preferably 0.9 to 1.1, preferably NaOH, Na ₂ CO ₃ , NH ₃ , MgO and / or MgCO ₃ . hydroxide or carbonate precipitated.

The oxidation then takes place, air being preferably used as the oxidizing agent. For this, who introduced 20 to 300 l of air per hour and liter of suspension. The result is a black germ suspension in which only magnetite (Fe ₃ O ₄ ) is detected by X-ray phase analysis (Siemens D-500) (ASTM no .: 19.0629). The germ suspension can then preferably be subjected to ripening at 70 to 100 ° C. for one to four hours.

For the pigment formation, a seed amount of 4 to 30 g / l, particularly preferably 7 to 20 g / l, calculated as Fe ₂ O ₃ , is preferably used. The pigment formation can be carried out by two methods. In the first case, metallic iron is added to the germ suspension, heated to 70 to 100 ° C., preferably 75 to 90 ° C., and oxidized with 0.2 to 50 l of air per hour and liter of suspension until the desired color is reached. This is achieved by multiplying the number of germs by a factor of 2.5 to 10, preferably 3 to 6.

In the second case, the germ suspension is 70 to 100 ° C, preferably heated to 75 to 90 ° C, iron (II) salt and alkali solution metered in and with 1 to 400 l air per  Hour and liter of suspension until the ge desired hue oxidized, the pH in Be ranges between 4 and 5.

The brine can be separated off by filtration and Wash or sedimentation. The red paste can be processed into slurries or dried and dried powdered pigments are ground.

Soft, color-pure iron oxide red pigments are obtained. Alpha-Fe ₂ O _{3 is} detected by X-ray phase analysis (ASTM No. 33.0664).

Color testing of pigments for applications in paint area was carried out in Alkydal L64 (commercial product of Bayer AG, alkyd resin with 63% linseed oil and 23% phthal acid anhydride, which increases viscosity by 5% Luvotix HT (commercial product from Lehmann & Voss) is added). The pigment volume concentration is 10%.

For testing the pigments for applications in building materials area (DIN 53237), heavy spar compacts were brought on does. For this purpose, 0.5 g pigment with 10 g heavy spar placed in a shaking glass with approx. 250 ml content. To Add 200 steel balls of 5 mm diameter was 3 minutes with an automatic round table shaker shaken. The mixture became one cylindrical body pressed.

The CIELAB data (DIN 6174) was determined with a color measuring device with integrating sphere (lighting condition  d / 8 °, standard illuminant C / 2 °) including the Surface reflection.

Table 1 contains the colorimetric data according to some pigments produced by the process according to the invention and the comparative values of some commercial products.

This is the measure of the color purity of the pigments Saturation (C *).

The pigments produced according to the invention have both in testing for paint and construction higher color saturations than that after hitherto customary processes (US-A 3 946 103) Direct red pigments (Bayferrox 510®, commercial product of Bayer AG) and that by calcination of black pigments (manufactured e.g. according to DE-A 28 26 941, DE-A 4 63 773) red pigments obtained (Bayferrox 105M®, Bayferrox 110®, Commercial product from Bayer AG).

Particularly high levels of red (a *) can be achieved in the paint that become an aesthetically pure Color impression lead.

The strong yellow streak (b *) in the building material also high proportion of red (a *) the desired aesthetics preserved brick red tones.

Pigments that multiply by a factor 1.0 to 1.5 are suitable for the On set as transparent brown pigments. With a germ  they can be multiplied by a factor of 1.5 to 4 as transparent or semi-transparent red pigments Ver find application.

The present invention also relates to the Ver application of the iron oxide red produced according to the invention pigments for coloring in paint, plastic, building materials and ceramics, both as powdered pigments as well as pastes or slurries.

Fig. 1, the electron micrograph shows a finely divided Magnetitkeims prepared by the novel method.

The invention is explained by way of example below. no limitation is to be seen here.  

example 1

22.3 l of an iron (II) sulfate solution from the titanium dioxide production with a concentration of 25 g / l FeSO ₄ are introduced. The temperature is 33 ° C. 1.35 l of a 4.75 n NaOH solution are added and then oxidized for 25 minutes with 52 l of air per hour and liter of suspension. A black seed suspension is obtained.

Example 2

22.3 l of an iron (II) sulfate solution from the titanium dioxide production with a concentration of 25 g / l FeSO ₄ are introduced. The temperature is 35 ° C. 1.35 l of a 4.75 n NaOH solution are added and then oxidized for 21 minutes with 52 l of air per hour and liter of suspension. A black seed suspension is obtained. This is heated to 80 ° C. and stirred for 2 hours with continuous gassing.

Example 3

To 4414 ml of the Keimsus pension produced according to Example 1, 23 ml of iron (II) sulfate solution (200 g / l FeSO ₄ ), 2563 ml of water and 450 g of metallic iron are added. After heating to 85 ° C is oxidized with 10 l of air per hour and liter of suspension. After 32 hours, the black germ suspension was converted into a color-pure red pigment. The duplication factor is 3.3. The suspension is filtered, washed free of salt, dried at 85 ° C. and the pigment obtained is ground.

Example 4

The procedure is as in Example 3. After 52 hours and a multiplication of germs by a factor of 4.6, the Sus filtered, washed salt-free, dried at 85 ° C net and the pigment obtained ground.

Example 5

105 ml of iron (II) sulfate solution (200 g / l FeSO ₄ ), 3067 ml of water and 450 g of metallic iron are added to 3828 ml of the germ suspension prepared according to Example 2. After heating to 85 ° C is oxidized with 7 l of air per hour and lither suspension. After 19 hours, the black-brown germ suspension was converted into a color-pure red pigment. The duplication factor is 3.5. The suspension is filtered, washed salt-free, dried at 85 ° C. and the pigment obtained is ground.

Claims (12)

1. Process for the preparation of pure iron oxide direct red pigments by precipitation of iron (II) salts with alkali solution and oxidation with oxygen-containing gases, addition of iron (II) salt solution and metallic iron or of iron (II) salt solution and alkali solution to the germ suspension thus obtained and oxidation with oxygen-containing gases until the desired color tone is reached, characterized in that a black magnetite nucleus suspension with a specific surface area <60 m ² / g and an average particle size <0.05 μm is used for pigment build-up. 2. The method according to claim 1, characterized in that for the preparation of the germ suspension

• a) an aqueous iron (II) sulfate solution with a concentration of 10 to 80 g / l, preferably 20 to 40 g / l, is introduced,
• b) with 0.8 to 1.5, preferably 0.9 to 1.1 equivalents of an alkaline precipitant is precipitated and
• c) for oxidation with air at a rate of 20 to 300 l per hour and liter of suspension is gassed intensively.

3. The method according to any one of claims 1 or 2, characterized in that the temperature at the Preparation of the germ suspension 30 to 80 ° C before is 30 to 50 ° C. 4. The method according to one or more of claims 1 to 3, characterized in that NaOH, Na ₂ CO ₃ , NH ₃ , MgO and / or MgCO ₃ is preferably used as the precipitation medium. 5. The method according to one or more of the claims 1 to 4, characterized in that the germs pension for 1 to 4 hours of maturation at 70 is subjected to up to 100 ° C. 6. The method according to one or more of claims 1 to 5, characterized in that the seed amount used for pigment build-up 4 to 30 g / l, calculated as Fe ₂ O ₃ , preferably 7 to 20 g / l, be. 7. The method according to one or more of the claims 1 to 6, characterized in that the germ suspension metallic iron and iron (II) salt added solution, this to 70 to 100 ° C, preferred 75 to 90 ° C, heated and with 0.2 to 50 l air per hour and liter of suspension to the desired Hue that increases the number of germs Factor 2.5 to 10, preferably 3 to 6, reached is oxidized.   8. The method according to one or more of the claims 1 to 7, characterized in that the germs pension to 70 to 100 ° C, preferably 75 to 90 ° C heated, iron (II) salt and alkali solution zudo and with 0.2 to 50 l air per hour and Liter of suspension to the desired shade, the with a multiplication of germs by a factor of 2.5 to 10, preferably 3 to 6, is reached, oxidized becomes. 9. Use of the according to one or more of the An Proverbs 1 to 8 produced iron oxide red pigments for coloring in paint, plastic, building materials or ceramic area. 10. Use of the iron oxide red pigments according to claim 9, characterized in that the pigment in the form pastes or slurries. 11. Use of the according to one or more of the An say 1 to 8 with a multiplication of germs around the Factor 1.0 to 1.5 pigments produced as transparent brown pigments. 12. Use of the according to one or more of the An say 1 to 8 with a multiplication of germs around the Factor 1.5 to 4 pigments produced as trans Parent or semi-transparent red pigments.