Particulate filler, preparation and use thereof
The present invention relates to a particulate filler which has a coating on support particles in each case surrounding the latter, which comprises a titanium dioxide doped with niobium and at least one further element, to a process for the preparation of a particulate filler of this type and to the use thereof, in particular as varistor filler having nonlinear electrical properties in coating compositions and moulding compounds.
1 . A particulate filler which consists of support particles and a coating in each case surrounding the support particles, wherein the support particles comprise at least one aluminium compound or silicon compound and the coating comprises a titanium dioxide doped with niobium and at least one further element, which at least one further element is Mn, Cr and/or Ce.
2 . The particulate filler according to claim 1 , wherein the support particles comprise aluminium oxide, silicon dioxide or an aluminosilicate.
3 . The particulate filler according to claim 1 , wherein the support particles consist of aluminium oxide, silicon dioxide, mullite, fly ash, kaolinite, pumice stone or perlite.
4 . The particulate filler according to claim 1 , wherein the support particles are in flake form, are spherical or have an isotropically irregular shape.
5 . The particulate filler according to claim 1 , which has a density of 1.5 to 4.5 g/cm 3 .
6 . The particulate filler according to claim 1 , wherein, besides niobium, the titanium dioxide is doped with at least two further elements of Mn, Cr and/or Ce.
7 . The particulate filler according to claim 1 wherein the doping is present in the titanium dioxide in an amount of 0.01 to 5 atom-%.
8 . The particulate filler according to claim 1 , which has an average particle size of 1 to 150 μm.
9 . The particulate filler according to claim 1 , wherein the coating is in granular form on the support particles.
10 . A process for preparing a particulate filler according to claim 1 , comprising providing the coating on the support particles, which support particles comprise at least one aluminium compound or silicon compound and which coating comprises at least one titanium compound, at least one niobium compound and at least one Mn, Cr and/or Ce compound in an aqueous suspension, and in wherein the support particles provided with the coating are subsequently dried and calcined, during which the coating is converted into a titanium dioxide in granular form which is doped with niobium and at least one further element, which at least one further element is Mn, Cr and/or Ce.
11 . The process according to claim 10 , wherein the support particles are in flake form, are spherical or have an isotropically irregular shape and comprise aluminium oxide, silicon dioxide or an aluminosilicate.
12 . The process according to claim 10 , wherein the support particles consist of aluminium oxide, silicon dioxide, mullite, fly ash, kaolinite, pumice stone or perlite.
13 . A moulding or coating composition pigmented by a particulate filler according to claim 1 .
14 . The melding moulding or coating composition according to claim 13 , wherein the moulding or coating composition comprises silicones, EPDM, polyurethanes, polyethylenes, epoxides, phenolic resins and/or a ceramic material.
15 . The moulding or coating composition according to claim 13 , wherein the particulate filler is present in the moulding or coating composition with a pigment volume concentration of 3-33% by vol., based on the volume of the moulding or coating composition.
16 . The moulding or coating composition according to claim 13 , wherein the particulate filler has nonlinear electrical properties in the moulding or coating composition.
17 . The particulate filler according to claim 1 , wherein the titanium dioxide is doped with one of the following combinations (a) Nb, Mn; (b) Nb, Mn, Cr; (c) Nb, Mn, Ce; (d) Nb, Cr; (e) Nb, Cr, Ce; (f) Nb, Ce; or (g) Nb, Mn, Cr, Ce.
18 . The particulate filler according to claim 1 , wherein the support particles consist of at least one aluminium compound or silicon compound.
19 . The particulate filler according to claim 1 , wherein the support particles consist of aluminium oxide, silicon dioxide or an aluminosilicate.
20 . The particulate filler according to claim 1 , wherein the titanium dioxide is doped with niobium and at least one further element, which at least one further element is Mn and/or Ce.