Iron oxide pigments containing al

Abstract

Aluminium-containing iron oxide pigments of the formula Fe2-xAlxO3 with x values from 0.01 to 0.25, characterized in that they possess an a* value of 30.5 to 32.5 CIELAB units and a b* value of 25.5 to 30.5 CIELAB units, measured in each case as full shade in the alkyd resin according to DIN EN ISO 787-25: 2007.

1 . Aluminium-containing iron oxide pigments of the formula Fe 2-x Al x O 3  with x values from 0.01 to 0.25, characterized in that they possess an a* value of 30.5 to 32.5 CIELAB units and a b* value of 25.5 to 30.5 CIELAB units, measured in each case as full shade in the alkyd resin according to DIN EN ISO 787-25: 2007. 
     
     
         2 . Pigments according to  claim 1 , characterized in that they possess a saturation Cab* of 39.8 to 44.6 CIELAB units, in each case as full shade, measured in the alkyd resin according to DIN EN ISO 787-25: 2007. 
     
     
         3 . Pigments according  claim 1 , characterized in that they have a specific surface area, by the BET method, of between 6.5 and 12.5 m 2 /g. 
     
     
         4 . Pigments according to  claim 1 , characterized in that the aluminium-containing iron oxide pigment is present in a haematite structure. 
     
     
         5 . Pigments according to  claim 1 , characterized in that the sum content of manganese and chromium is less than 500 ppm, based on the pigment. 
     
     
         6 . Pigments according to  claim 1 , characterized in that the amount of magnesium is less than 500 ppm, based on the pigment. 
     
     
         7 . Pigments according to  claim 1 , characterized in that the pigments possess a water content of less than 0.8 wt %. 
     
     
         8 . Pigments according to  claim 1 , characterized in that the pigments have an organic and/or inorganic coating, more particularly in an amount of 0.01 to 3 wt %, based on the pigment. 
     
     
         9 . Pigments according to  claim 1 , characterized in that they have a heat stability measured in HDPE polyethylene at 1% pigmentation, determined according to DIN EN 12877-2 by a change (ΔC ab *) in the saturation (C ab *) of less than 3 CIELAB units, on temperature increase from 200 to 320° C. 
     
     
         10 . Pigments according to  claim 1 , characterized in that in the formula the Al index x is from 0.01 to 0.10, more particularly from 0.025 to 0.075. 
     
     
         11 . Pigments according to  claim 1 , characterized in that in the formula the Al index x is from 0.11 to 0.25, more particularly from 0.12 to 0.15. 
     
     
         12 . Process for producing the aluminium-containing haematite pigments according to  claim 1 , comprising at least the steps of a) precipitation, b) oxidation and c) calcination, characterized in that:
 a1) an aqueous solution comprising ions of iron, of sulfate and of aluminium, the molar ratio of iron ions to Al ions being 199:1 to 7:1, is reacted with an alkali metal hydroxide, more particularly NaOH, as alkaline compound, with the aqueous solution comprising ions of iron, of sulfate and of aluminium being metered into the initial charge of the alkaline compound, or   a2) an aqueous solution comprising ions of iron and of sulfate is reacted with an alkali metal hydroxide, more particularly NaOH, as alkaline compound, and with at least one aluminium compound, more particularly sodium aluminate, with the molar ratio of iron in the solution to aluminium in the aluminium compound being 199:1 to 7:1 and with the alkaline compound being introduced as an initial charge with at least one aluminium compound, and the aqueous solution comprising ions of iron and of sulfate being metered in,   b) the aqueous suspension obtained after step a1) or a2) is oxidized in the presence of an oxidizing agent, and   c) the oxidation product obtained after b) is calcined at a temperature of 500 to 1100° C. in an oxidizing atmosphere.   
     
     
         13 . Process according to  claim 12 , characterized in that the aqueous solution comprising ions of iron, of sulfate and of aluminium in step a1) has an Fe(III) fraction of 5 to 30 mol %, more particularly 10 to 20 mol % Fe(III), based on the total amount of iron in the solution. 
     
     
         14 . Process for the colouring of pastes, paints, plastics, paper and building materials, wherein the pigments according to  claim 1  are utilized. 
     
     
         15 . Pigments according to  claim 1 , characterized in that they possess a saturation Cab* of 39.8 to 44.6 CIELAB units, in each case as full shade, with illuminant D65/10°, measured in the alkyd resin according to DIN EN ISO 787-25:2007. 
     
     
         16 . Pigments according to  claim 1 , characterized in that the sum content of manganese and chromium is less than 100 ppm, based on the pigment. 
     
     
         17 . Pigments according to  claim 1 , characterized in that the amount of magnesium is less than 100 ppm, based on the pigment. 
     
     
         18 . Pigments according to  claim 1 , characterized in that the pigments possess a water content of less than 0.5 wt %. 
     
     
         19 . Pigments according to  claim 1 , characterized in that they have a heat stability measured in HDPE polyethylene at 1% pigmentation, determined according to DIN EN 12877-2 by a change (ΔC ab *) in the saturation (C ab *) of less than 1.5 CIELAB units, on temperature increase from 200 to 320° C. 
     
     
         20 . Process according to  claim 12  for producing the aluminium-containing haematite pigments according to  claim 1 , comprising at least the steps of a) precipitation, b) oxidation and c) calcination, characterized in that:
 a1) an aqueous solution comprising ions of iron, of sulfate and of aluminium, the molar ratio of iron ions to Al ions being 199:1 to 7:1, is reacted with an alkali metal hydroxide, more particularly NaOH, as alkaline compound, with the aqueous solution comprising ions of iron, of sulfate and of aluminium being metered into the initial charge of the alkaline compound in the form of its aqueous solution, or 
 a2) an aqueous solution comprising ions of iron and of sulfate is reacted with an alkali metal hydroxide, more particularly NaOH, as alkaline compound, and with alkali metal aluminate, more particularly sodium aluminate, with the molar ratio of iron in the solution to aluminium in the aluminium compound being 199:1 to 7:1 and with the alkaline compound being introduced as an initial charge with an alkali metal aluminate solution, and the aqueous solution comprising ions of iron and of sulfate being metered in, 
 d) the aqueous suspension obtained after step a1) or a2) is oxidized in the presence of an oxidizing agent, and 
 e) the oxidation product obtained after b) is calcined at a temperature of 500 to 1100° C. in an oxidizing atmosphere.