Heat-stable zinc ferrite colour pigments, process for preparing them and their use
View Patent ↗The present invention relates to zinc ferrite colour pigments, including a process for preparing and using them and, more particularly, the present invention relates to light-coloured zinc ferrite colour pigments having enhanced thermal stability, a magnesium content of from 0.01%-0.4% by weight, a color difference ΔE* according to DIN 53 772 at 260° C. of <3.0, a color difference ΔE* according to DIN 53 772 at 300° C. of <5.0, and a lightness of L*, measured in PE-HD full shade according to DIN 55 772 of >52.5.
1. A zinc ferrite colour pigment having a magnesium content of from 0.3% to 4% by weight wherein the pigment has a lightness L*, measured in PE-HD full shade according to DIN 53 772 of >52.5.
2. The zinc ferrite colour pigment according to claim 1 , wherein the magnesium content s from 0.3% to 0.6% by weight.
3. The zinc ferrite colour pigment according to claim 1 , wherein the pigment has a colour difference ΔE* according to DIN 53 772 at 260° C. of <3.0.
4. The zinc ferrite colour pigment according to claim 1 , wherein the pigment has a colour difference ΔE* according to DIN 53 772 at 260° C. of 2.4.
5. The zinc ferrite colour pigment according to claim 1 , wherein the pigment has a colour difference ΔE* according to DIN 63 772 at 300° C. of <5.0.
6. The zinc ferrite colour pigment according to claim 1 , wherein the pigment has a colour difference ΔE* according to DIN 53 772 at 300° C. of <4.0.
7. The zinc ferrite colour pigments according to claim 1 , wherein the pigment has a lightness L*, measured in PE-HD full shade according to DIN 53 772 of >53.5.
8. A process for preparing the zinc ferrite colour pigment according to claim 1 , comprising:
admixing a starting solution or raw-materials mixture comprising goethite which gives rise to an initial mixture of zinc oxide and iron oxide corresponding to the composition of the zinc ferrite colour pigment; and
calcining with one or more magnesium compounds in amounts effective to produce from 0.1 to 4% by weight of magnesium, after said calcining, in the zinc ferrite colour pigment.
9. The process according to claim 8 , wherein after said calcining there is from 0.05 to 0.6% by weight of magnesium in the zinc ferrite colour pigment.
10. A process for colouring baking enamels, coil coating materials, plastics, sand granules, lime sandstones, enamels or ceramic glazes, comprising:
adding the zinc ferrite colour pigment according to claim 1 to said baking enamels, coil coating materials, plastics, sand granules, lime sandstones, enamels or ceramic glazes.