Title of Invention

TITANIUM DIOXIDE PIGMENT PARTICLES WITH DOPED DENSE SIO2 SKIN AND METHOD FOR THE PRODUCTION THEREOF

Abstract The invention relates to titanium dioxide pigment particles which have inproved photo stability, their surface being coated with a dense SiO2 skin that is doped with at least one doping element. The SiO2 skin is characterized in that the doping with the at least one doping element reduces the energy level densities in the valence band and/or in the conduction band in the vicinity of the band gap or that additional energy levels in the band gap are produced. The doped dense SiO2 skin is applied using known wet-chemical methods or is applied in the gas phase to the surface of the titanium dioxide particles. Particularly suitable doping elements are Sn, Sb, In, Ge, Y, Nb, F, Mn, Cu, Mo, Cd, Ce, W and Bi. The following known doping elements AI, B, Ge, Mg, Nb, P, Zr for the gas phase method and Ag, AI, B, Ba, Be, Ca, Cd, Co, Cr, Cu, Mg, Mn, Ni, Nb, Sn, Sr, Ti, Zn, Zr for the wet-chemical method are excluded from the invention
Full Text FORM 2
THE PATENT ACT 1970 (39 of 1970)
The Patents Rules, 2003 COMPLETE SPECIFICATION See Section 10, and rule 13
1. TITLE OF INVENTION
TITANIUM DIOXIDE P WENT PARTICLES WITH DOPED DENSE SI02 SKIN AND METHOD FOR THE PRODUCTION THEREOF



APPLICANT (S.)
a) Name
b) Nationality
c) Address

KRONOS INTERNATIONAL, INC GERMAN Company POSTFACH 10 07 20, 51307 LEVERKUSEN, GERMANY

PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in'which it is to be performed : -


TRANSLATION (VERIFICATION)
RE: INDIAN PATENT APPLICATION NO. (BASED ON PCT/EP2007/000762)
I, "Michaela- Kunigkeit of Bergerhof 69, 42799 Leichlingen, Germany, hereby declare that I am conversant with German and English languages, I believe the attached copy in English of the document, the International Application No. PGT/EP2007/000762, entitled "TITANIUM DIOXIDE PIGMENT PARTICLES WITH DOPED, DENSE Si02 SKIN AND METHODS FOR THEIR MANUFACTURE", is a true and complete translation of the said International Application.
I hereby declarem that all;statements made herein are true and made on information which I believe to: be true.
Dated this 27th day of may 2008.
Name: Michaela Kunigkeit

Field of the Invention
The invention relates to titanium dioxide pigment particles whose surface is provided with a dense silicon dioxide skin doped with doping elements, and methods for their manufacture. The titanium dioxide pigment particles according to the invention display improved photostability.
Technological Background of the Invention
Because of its high refractive index, titanium dioxide is used as a high-quality pigment in many sectors, e.g. plastics, coatings, paper and fibres. However, titanium dioxide is photoactive, meaning that undesired photocatalytic reactions occur as a result of UV absorption, leading to degradation of the pigmented material [The Chemical Nature of Chalking in the Presence of Titanium Dioxide Pigments, H. G. Volz, G. Kaempf, H. G. Fitzky, A. Klaeren, ACS Symp. Ser. 1981, 151, Photodegradation and Photostabilization of Coatings].
In this context, titanium dioxide pigments absorb light in the near ultraviolet range, the result being that electron-hole pairs are produced, which lead to the formation of highly reactive radicals on the titanium dioxide surface. The radicals produced in this way result in binder degradation in organic media. It is known from experimental investigations that hydroxyl ions play a dominant role in the photocatalytic process [Photocatalytic Degradation of Organic Water Contaminants: Mechanism Involving Hyroxyl Radical Attack , C. S. Turchi, D. F. Ollis, Journal of Catalysis 122,1990,178-192].
It is known that the photoactivity of TiO2 can be reduced by doping the Ti02 particles (e.g. with aluminium) or by means of inorganic surface treatment (e.g. by coating with oxides of silicon and/or aluminium and/or zirconium) [Industrial Inorganic Pigments, ed. by G. Buxbaum, VCH, New York 1993, p. 58 - 60]. In particular, several patents describe the application of the most dense possible, amorphous layer of Si02 to the particle surface, this being known as a "dense skin". The purpose of this skin is to prevent the formation of free radicals on the particle surface.
Wet-chemical methods for production of a dense S1O2 skin, and of a further AI2O3 coating on inorganic particles, particularly on Ti02, are described in patents US 2,885,366, US RE. 27,818 and US 4,125,412. EP 0 245 984 Bl indicates a method which, as a result of simultaneous addition of a solution containing Na2Si03 and a solution containing B203, can be performed at relatively low temperatures of 65 to 90 °C. Si02 dense-skin treatments are also carried out in order to increase the abrasion resistance of glass fibres coated in this way and reduce the slipping properties of the fibres in the products manufactured. In this connection, US 2,913,419 describes a wet-chemical method in which silicic acid is precipitated onto the particle surface together with polyvalent metal ions, such as Cu, Ag, Ba, Mg, Be, Ca, Sr, Zn, Cd, Al, Ti, Zr, Sn, Pb, Cr, Mn, Co, Ni.
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The method according to DE 10 2004 037 271 Al makes it possible to increase the photostability of dense-skin TiO2 pigments. It is based on the incorporation of Sn, Ti or Zr in the SiO2 skin applied by a wet-chemical process.
In addition to the known wet-chemical methods for coating the surface of TiC>2 particles, there are also methods in which the dense Si02 skin is deposited from the gas phase. In this case, during titanium dioxide production by the chloride process, a silicon compound, preferably SiCL4, is added to the Ti02 particle stream with a temperature of over 1,000 °C, such that a uniform, dense SiO2 layer is formed on the particle surface.
EP 1 042 408 Bl describes a gas-phase method for surface coating with Si and B, P, Mg, Nb or Ge oxide.
Object and Summary of the Invention
The object of the present invention is to create titanium dioxide pigment particles, coated with a dense SiO2 skin, that display improved photostability compared to the known dense-skin pigment particles. The object of the invention is furthermore to indicate a method for manufacturing this pigment.
The object is solved by titanium dioxide pigment particles, whose surface is coated with a dense SiO2 skin, deposited from the gas phase and doped with at least one doping element and where the SiO2 skin is characterised in that due to doping with at least one doping element the energy density states in the valence band and/or in the conduction band near the band edge are decreased or additional energy states are generated in the band gap and whereby doping elements selected from the group Al, Be, Ge, Mg, Nb, P and Zr are excluded.
The object is furthermore solved by titanium dioxide pigment particles, whose surface is coated with a dense SiO2 skin, deposited from the gas phase and doped with at least one doping element, whereby the doping elements are selected from the group Sn, Sb, In, Y, Zn, F, Mn, Cu, Mo, Cd, Ce, W and Bi as well as mixtures thereof. The object is furthermore solved by titanium dioxide pigment particles, whose surface is coated with a dense Si02 skin, produced in a wet chemical process and doped with at least one doping element and where the Si02 skin is characterised in that due to doping with at least one doping element the energy density states in the valence band and/or in the conduction band near the band edge are decreased or additional energy states are generated in the band gap and whereby doping elements selected from the group Ag, Al, B, Ba, Be, Ca, Cd, Co, Cr, Cu, Mg, Mn, Ni, Pb, Sn, Sr, Ti, Zn and Zr are excluded.
The object is furthermore solved by titanium dioxide pigment particles, whose surface is coated with a dense Si02 skin, produced in a wet chemical process and doped with at least one doping element, whereby the doping elements are selected from the group Sb, In, Ge, Y, Nb, F, Mo, Ce, W and Bi as well as mixtures thereof. The object is furthermore solved by a method for manufacturing titanium dioxide
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pigment particles whose surface is coated with a dense SiO2 skin doped with at least one doping element, comprising the steps:
a) Reaction, in the gas phase, of titanium tetrachloride with an aluminium halide and a gas containing oxygen in a reactor at a temperature above 1,000 °C, in order to create a particle stream containing TiO2 particles,
b) Contacting of the particle stream with at least two oxide precursor compounds, where the first oxide precursor compound is a silicon compound and the second oxide precursor compound is selected from the group consisting of oxide precursor compounds of Sn, Sb, In, Y, Zn, Mn, Cu, Mo, Cd, Ce, W, Bi and precursor compounds of F, as well as mixtures thereof,
c) Cooling of the particle stream, in order to create pigment particles that are coated with a dense Si02 skin doped with at least one doping element, where the doping elements are selected from the group Sn, Sb, In, Y, Zn, F, Mn, Cu, Mo, Cd, Ce, W and Bi, as well as mixtures thereof.
Finally a further solution of the object consists in a method for manufacturing titanium dioxide pigment particles whose surface is coated with a dense Si02 skin doped with at least one doping element, comprising the steps:
a) Provision of an aqueous suspension of TiO2 particles with a pH value in excess of 10,
b) Addition of an aqueous solution of an alkaline silicon component and at least one aqueous solution of a component containing a doping element, where the doping element is selected from the group Sb, In, Ge, Y, Nb, F, Mo, Ce, W and Bi, as well as mixtures thereof,
c) Deposition of a dense SiO2 skin doped with at least one doping element on the surface of the particles by lowering the pH value of the suspension to a value below 9, preferably to below 8, where the doping elements are selected from the group Sb, In, Ge, Y, Nb, F, Mo, Ce, W and Bi, as well as mixtures thereof.
Further advantageous embodiments of the invention are indicated in the sub-claims.
The subject matter of the invention is coated titanium dioxide pigments that are further improved in terms of their photostability.
Description of the Invention
The pigments according to the invention contain, in a dense skin on the titanium dioxide particle surface, 0.1 to 6.0% by weight, preferably 0.2 to 4.0% by weight, silicon, calculated as Si02, and 0.01 to 3.0% by weight, preferably 0.05 to 2.0% by weight, doping element, calculated as oxide or in the case of F calculated as element and referred to the total pigment.
In a preferred embodiment, the particles are coated with an additional layer of 0.5 to 6.0% by weight, preferably 1.0 to 4.0% by weight, aluminium oxide or hydrous aluminium oxide, calculated as AI2O3 and referred to the total pigment. The titanium dioxide particles are preferably rutile.
Here and below, "doping element" is to be taken to mean the respective element as atom or ion or a respective compound like an oxide, where appropriate. In the
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context of the description of the coatings produced by the wet-chemical process, the term "oxide" is to be taken, here and below, to also mean the corresponding hydrous oxides or corresponding hydrates. All data disclosed below regarding pH value, temperature, concentration in % by weight or % by volume, etc., are to be interpreted as including all values lying in the range of the respective measuring accuracy known to the person skilled in the art.
The invention is based on the fact that, in order to increase the photostability, the photocatalytic process must be interrupted in a suitable manner, i.e. that the production of highly reactive radicals by excited electron-hole pairs must be made more difficult. This can be achieved by utilising various mechanisms, e.g. by increasing the recombination rate of the electron-hole pairs, or by building up an energetic barrier on the pigment surface.
A dense and uniformly applied SiO2 skin already builds up an energetic barrier on the Ti02 surface, as detectable by a reduced energy state density near the band edge in the valence band and in the conduction band of the coated TiO2 surface, compared to the untreated TiC>2 surface. Surprisingly, doping of the Si02 skin with selected elements leads to a further reduction in the energy state densities near the band edge, thus raising the energetic barrier and thus further improving the photostability of the TiO2 pigment coated in this way.
Additional energy states within the band gap between valence band and conduction band promote the recombination of electron-hole pairs. Doping of the SiO2 layer with selected elements generates these energy states and thus effects also an improvement in photostability compared to an undoped SiO2 layer.
The elements Sn, Sb, In, Ge, Y, Zr, Zn, Nb, F, Mn, Cu, Mo, Cd, Ce, W und Bi have proven to be suitable doping components. The doped SiO2 skin can be applied both by the wet-chemical method and by the gas-phase method. It is, however, known that the gas-phase method is generally capable of applying a more uniform skin than the wet-chemical method.
The invention also comprises the doping of the dense SiO2 skin with further doping elements for which the energy state densities have not been calculated yet, the calculation of which, however, can be easily performed as will be shown below. All doping elements, which generate the energy states in the doped SiO2 layer according to the invention and have not been found so far by chemical experimentation, are claimed in this invention. Known doping elements which are not comprised by the invention, are AI, B, Ge, Mg, Nb, P, Zr for the - dry - gas phase process and Ag, Al, B, Ba, Be, Ca, Cd, Co, Cr, Cu, Mg, Mn, Ni, Nb, Sn, Sr, Ti, Zn, Zr for the wet chemical process.
In addition, suitable combinations of two or more doping elements can be found by calculation of the total energy state densities which are based on the interaction of the energy states of the individual elements. Such advantageous combinations are easily determined by the methods of the present invention in contrast to time consuming and costly chemical experiments of the prior art.
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An example of the invention is described below with the help of Figures 1 to 18.
Figure 1 shows the energy states at the transition from the atom to the solid (taken
from: P.A. Cox, "The Electronic Structure and Chemistry of Solids", Oxford Science
Publications 1987, p. 13).
Figure 2 shows the energy state density of the TiO2 surface without and with SiO2
coating.
Figure 3 shows the energy state density of the TiO2 surface with SiO2 coating and
with Sn-doped SiC>2 coating.
Figure 4 shows the energy state density of the TiO2 surface with SiO2 coating and
with Sb-doped SiO2 coating.
Figure 5 shows the energy state density of the TiO2 surface with SiO2 coating and
with In-doped SIO2 coating.
Figure 6 shows the energy state density of the TiO2 surface with SiO2 coating and
with Ge-doped SiO2 coating.
Figure 7 shows the energy state density of the TiO2 surface with SiO2 coating and
with Y-doped SiO2 coating.
Figure 8 shows the energy state density of the TiO2 surface with SiO2 coating and
with Nb-doped SiO2 coating.
Figure 9 shows the energy state density of the TiO2 surface with SiO2 coating and
with F-doped SiO2 coating.
Figure 10 shows the energy state density of the TiO2 surface with SiO2 coating and
with Mn-doped SiO2 coating.
Figure 11 shows the energy state density of the TiO2 surface with SiO2 coating and
with Cu-doped SiO2 coating.
Figure 12 shows the energy state density of the TiO2 surface with SiO2 coating and
with Mo-doped SiO2 coating.
Figure 13 shows the energy state density of the T1O2 surface with SiO2 coating and
with Cd-doped SiO2 coating.
Figure 14 shows the energy state density of the T1O2 surface with SiO2 coating and
with Ce-doped SiO2 coating.
Figure 15 shows the energy state density of the TiO2 surface with SiO2 coating and
with W-doped SiO2 coating.
Figure 16 shows the energy state density of the TiO2 surface with SiO2 coating and
with Bi-doped SiO2 coating.
Figure 17 shows the energy state density of the TiO2 surface with SiO2 coating and
with Mg-doped SiO2 coating.
Figure 18 shows the energy state density of the TiO2 surface with SiO2 coating and
with Al-doped SiO2 coating
The energy state densities were calculated quantum-mechanically with the help of the CASTEP software package (Version 4.6, 1 June 2001) from Accelrys Inc., San Diego. The calculations were performed using the CASTEP density functional code in the LDA (local density approximation). Detailed information has been published by V. Milman et al. in: International Journal of Quant. Chemistry 77 (2000), p. 895 to 910.
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The following valence states, including the semi-core states, were used for titanium:
3s, 3p, 3d, 4s and 4p. The valence states 2s and 2p were used for oxygen, and the
valence states 3s and 3p for silicon. For the doping elements, the semi-core states 4d
or 4s and 4p or 2p were included for indium, yttrium and magnesium. The basic set
used for the doping elements was as follows:
Sn: 5s, 5p, 6s, 6p, 7s
Sb: 5s, 5p, 6s, 6p, 7s
In: 4d, 5s, 5p, 6s, 6p, 7s
Ge: 4s, 4p, 4d
Y: 4s, 4p, 4d, 5s, 5p
Nb: 4s, 4p, 4d, 5s, 5p
F: 2s, 2p
Mn: 3d, 4s, 4p
Cu: 3d, 4s, 4p
Mo: 4s, 4p, 4d, 5s, 5p
Cd: 4d, 5s, 5p, 6s, 6p
Ce: 4f, 5s, 5p, 6s, 6p, 7s, 7p, 8s
W: 5d, 6s, 6p
Bi: 6s, 6p, 7s, 7p, 8s
Mg: 2p, 3s, 3p
Al: 3s, 3p
The kinetic energy cut-off for the plane waves was 380 eV. Structural geometric optimisation was not performed, since the mathematical model could be evaluated and confirmed on the basis of known experimental results (coating with Sn, Al, Zr and Zn). Thus, the model calculations yield sufficient accuracy for examination of the photostability.
The state density calculations were based on a grid according to the Monkhorst-Pack scheme. The surface calculations were performed in accordance with the "slab model method" with a vacuum thickness of 10 A.
Examples
The invention is explained on the basis of Examples 1 to 14 (doping of the SiO2 layer with one of the doping elements Sn, Sb, In, Ge, Y, Nb, F, Mn, Cu, Mo, Cd, Ce, W or Bi), Reference Example 1 (pure Si02 layer), Reference Example 2 (doping of the SiO2 layer with Mg) and Reference Example 3 (doping of the SiO2 layer with Al).
The calculation for Reference Example 1 is based on complete coverage of a TiO2 (110) surface with an SiO2 monolayer. In this context, the unit cell comprises 52 atoms (TisS18O36). Applied to the pigment, the calculated monomolecular coverage with SiO2 with a layer thickness of approximately 0.2 nm corresponds to a percentage by weight of roughly 0.3% by weight SiO2, referred to TiO2. The percentage by weight was calculated on the basis of the following values: typical, value of the specific surface (to BET) for TiO2 particles manufactured by the chloride process: 6.2 m2/g; thickness of the monomolecular layer: 0.2 nm; density of the SiCh layer: 2.2 g/cm3.
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Examples 1 to 14 and Reference Example 2 and 3 describe coverage of the TiCb
surface with a monomolecular SiO2 layer doped at an atomic ratio of 1 (doping
element X) : 7 (Si), i.e. the unit cell comprises TisSi7Xi036. Applied to the TiO2
pigment, this results in the following percentages by weight of the doping elements,
calculated as oxide and referred to TiO2.
Example 1: roughly 0,10 % by weight SnO2
Example 2: roughly 0.09 % by weight Sb2O3,
Example 3: roughly 0.09 % by weight In2O3,
Example 4: roughly 0.07 % by weigh. GeO2,
Example 5: roughly 0.14 % by weight Y2O3,
Example 6: roughly 0.09 % by weight Nb2O3,
Example 7: roughly 0.01 % by weight F3,
Example 8: roughly 0.06 % by weight MnO2,
Example 9: roughly 0.06 % by weight CuO,
Example 10: roughly 0.10 % by weight M0O3,
Example 11: roughly 0.09 % by weight CdO,
Example 12: roughly 0.12 % by weight CeO2,
Example 13: roughly 0.16 % by weight WO3,
Example 14: roughly 0.09 % by weight Bi2O3,
Reference Example 2: roughly 0.03 % by weight MgO;
Reference Example 3: roughly 0.04 % by weight AI2O3.
Results
The result of the quantum-mechanical CASTEP calculations is the electronic structure. This can be analysed in the form of band structures (energy bands spatially resolved) or the state densities (integrated energy states). Figure 1 shows a simplified block diagram (d) of the electronic structure. The block diagram reflects only the energy bandwidth and position of the energy band. The state density (e) is used for the energy state distribution within the energy band. Figure 2 shows the effect of a pure, undoped SiO2 coating (Reference Example 1) on the photoactivity of the TiO2: the calculated state density of the pure TiO2 (110) surface is shown as a broken line, that of the SiO2 coated surface as a solid line. The positive effect of the Si2 coating on photostability is partly based on the reduction of the state density near the band edge in the conduction band (CB), compared to the uncoated TiO2 surface, this reducing the transfer of electron-hole pairs to the surrounding matrix. At the same time, the positive effect is intensified by the fact that there is additionally a reduction in the state density near the band edge in the valence band (VB).
Figure 3 shows the effect of doping the SiO2 layer with Sn (Example 1) on the state densities, compared to the pure SiO2 coating. In this case, there is a further reduction in the VB state density, this leading to improved photostability.
Figures 4 to 8 show the respective effect of doping the S1O2 layer with Sb (Example 2, Fig. 4), In (Example 3, Fig. 5), Ge (Example 4, Fig. 6), Y (Example 5, Fig. 7) and Nb (Example 6, Figure 8). Surprisingly, a reduction in the VB state density near the band edge can be seen in each case, meaning that these coatings lead to an increase in photostability.
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Similar doping of the SiO2 layer with the elements Zr or Zn likewise leads to improved stability compared to an undoped SiC>2 layer.
Figures 9 to 16 show the respective effect of doping the SiO2 layer with F (Example 7, Figure 9), Mn (Example 8, Figure 10), Cu (Example 9, Figure 11), Mo (Example 10, Figure 12), Cd (Example 11, Figure 13), Ce (Example 12, Figure 14), W (Example 13, Figure 15) and Bi (Example 14, Figure 16).
Figure 17 shows the effect of doping the SiO2 layer with Mg (Reference Example 2) on the state densities. In this case, there is an increase in the VB state density, meaning that doping of the SiO2 layer with Mg results in a loss of photostability. Figure 18 shows the effect of doping the SiO2 layer with Al (Reference Example 3) on the state densities. In this case, there is likewise an increase in the VB state density, meaning that doping of the SiO2 layer with Al results in a loss of photostability.
The results of the state density calculations correlate favourably with the data of photostability determined with experimentally doped samples. Thus, by means of the calculation method described useful doping elements for increasing the photostability of TiO2 pigments with dense SiO2 skin (dense skin pigments) can be predicted more precisely than by means of the "trial and error method" of chemical experiments. Based on the present invention the person skilled in the art may calculate and predict the suitability of further doping elements or combinations of doping elements for improvement of the photostability of dense-skin pigments which have not been mentioned in the prior art or in this specification. The inventors are aware of the following doping elements which have been found by experiments and have been published in the prior art: Al, B, Ge, Mg, Nb, P, Zr for the gase phase process and Ag, Al, B, Ba, Be, Ca, Cd, Co, Cr, Cu, Mg, Mn, Ni, Nb, Sn, Sr, Ti, Zn, Zr for the wet chemical process.
Process control
Methods for coating titanium dioxide particles with dense SiO2 as such are known.
The traditional processes work via the aqueous phase. To this end, a TiO2 particle
suspension is produced, mixed with a dispersant where appropriate, and wet-milled
where appropriate. The dense SiOi skin is customarily precipitated by adding alkali
metal-silicate solutions and appropriate pH value control.
The doping element is added in the form of a salt solution, together with the silicate
solution or separately before or after addition of the silicate solution. The person
skilled in the art is familiar with the suitable compounds and necessary quantities
for controlling the pH value in order to produce a dense skin.
Doping of the dense SiO2 skin according to the invention can, for example, be
achieved by adding the following salts to the suspension, where this compilation is
not to be interpreted as a restriction of the invention.
Doping with Sb: antimony chloride, antimony chloride oxide, antimony fluoride,
antimony sulphate
Doping with In: indium chloride, indium sulphate
Doping with Ge: germanium chloride, germanates
Doping with Y: yttrium chloride, yttrium fluoride
Doping with Nb: niobium chloride, niobates
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Doping with F: fluorine hydrogen, fluorides
Doping with Mn: manganese chloride, manganese sulphate
Doping with Cu: copper chloride, copper sulphate
Doping with Mo: molybdenum chloride, molybdates
Doping with Cd: cadmium chloride, cadmium sulphate
Doping with Ce: cerium nitrate, cerium sulphate
Doping with W: wolframates
Doping with Bi: bismuth nitrate, bismuth sulphate
In a particularly preferred embodiment, an outer layer of hydrous aluminium oxide is additionally applied to the particles by known methods.
In another embodiment of the invention, the dense SiO2 skin is deposited on the particle surface from the gas phase. Various methods are known for this purpose. For example, coating can be performed in a fluidised bed at temperatures below roughly 1,000 °C Methods of this kind are described in US 3,552,995, GB 1 330 157 or US 2001 0041217 Al.
Alternatively, coating takes place in a tubular reactor directly following formation of the TiO2 particles in the chloride process; these methods are described, for example, in patents or patent applications WO 98/036441 Al, EP 0 767 759 Bl, EF 1042 408 Bl and WO 01/081410 A2. For coating in a tubular reactor, the precursor compound used for the SiO2 is customarily a silicon halide, particularly SiO2, which is generally introduced downstream of the point where the reactants TiCI4 and AICI3 are combined with the oxygen-containing gas. For instance, WO 01/081410 A2 indicates that the silicon halide is added at a point where the T1O2 formation reaction is at least 97 % complete. In any case, the temperatures at the point of introduction should be above 1,000 °C, preferably above 1,200 °C. The SiO2 precursor compound is oxidised and deposited on the surface of the TiO2 particles in the form of a dense silicon dioxide skin. In contrast to the wet-chemical method, water and hydrate-free oxide layers are formed during gas-phase treatment, these adsorbing hydroxyl ions and water molecules only on the surface.
The doping element is likewise added to the particle stream as a precursor compound, either in parallel with the SiO2 precursor compound, or upstream or downstream. Here, too, the temperature of the particle stream at the point of introduction must be above 1,000 °C, preferably above 1,200 °C. The following compounds are suitable precursor compounds for the various doping metal oxides, although this compilation is not to be interpreted as a restriction of the invention: Doping with Sn: tin halide, such as tin chloride Doping with Sb: antimony halide, such as antimony chloride Doping with In: indium halide, such as indium chloride Doping with Y: yttrium halide, such as yttrium chloride Doping with Zr: zirconium halide, such as zirconium chloride Doping with Zn: zinc halide, such as zinc chloride Doping with Nb: niobium halide, such as niobium chloride Doping with F: fluorine, fluorine hydrogen, fluorides Doping with Mn: manganese chloride Doping with Cu: copper chloride
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Doping with Mo: molybdenum chloride Doping with Cd: cadmium chloride Doping with Ce: cerium chloride Doping with W: tungsten chloride Doping with Bi: bismuth chloride
In a particularly preferred embodiment, an outer layer of aluminium oxide is additionally applied to the particles by introducing a suitable aluminium oxide precursor compound, such as AlCI3, into the particle stream farther downstream.
Finally, the titanium dioxide pigments provided with the doped, dense SiO2 skin can be further treated by known methods, regardless of whether they were coated in a suspension or in the gas phase. For example, further inorganic layers of one or more metal oxides can be applied. Moreover, further surface treatment with nitrate and/or organic surface treatment can be performed. The compounds known to the person skilled in the art for organic surface treatment of titanium dioxide pigment particles are also suitable for organic surface treatment of the particles according to the invention, e.g. organosilanes, organosiloxanes, organophosphonates, etc., or polyalcohols, such as trimethylethane (r IE) or trimethylpropane (TMP), etc.
The titanium dioxide pigment particles according to the invention are suitable for use in plastics, paints, coatings and papers. They can also be used as a starting basis for a suspension for producing paper or coatings, for example.
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WE CLAIM:
1. Titanium dioxide pigment particles,
whose surface is coated with a dense SiO2 skin, deposited from the gas phase and doped with at least one doping element and where the SiO2 skin is characterised in that
due to doping with at least one doping element the energy density states in the valence band and/or in the conduction band near the band edge are decreased or additional energy states are generated in the band gap and whereby doping elements selected from the group Al, Be, Ge, Mg, Nb, P and Zr are excluded.
2. Titanium dioxide pigment particles,
whose surface is coated with a dense SiO2 skin, deposited from the gas phase and doped with at least one doping element, whereby
the doping elements are selected from the group Sn, Sb, In, Y, Zn, F, Mn, Cu, Mo, Cd, Ce, W and Bi as well as mixtures thereof.
3. Titanium dioxide pigment particles,
whose surface is coated with a dense SiO2 skin, produced in a wet chemical process and doped with at least one doping element and where the SiO2 skin is characterised in that
due to doping with at least one doping element the energy density states in the valence band and/or in the conduction band near the band edge are decreased or additional energy states are generated in the band gap and whereby doping elements selected from the group Ag, Al, B, Ba, Be, Ca, Cd, Co, Cr, Cu, Mg, Mn, Ni, Pb, Sn, Sr, Ti, Zn and Zr are excluded.
4. Titanium dioxide pigment particles,
whose surface is coated with a dense SiO2 skin, produced in a wet chemical process and doped with at least one doping element, whereby the doping elements are selected from the group Sb, In, Ge, Y, Nb, F, Mo, Ce, W and Bi as well as mixtures thereof.
5. Titanium dioxide pigment particles according to one or more of Claim 1 to 4,
characterised in that
they are coated with a further layer of aluminium oxide or hydrous aluminium oxide.
6. Titanium dioxide pigment particles according to one or more of Claims 1 to 4,
characterised in that
the silicon content of the dense skin is 0.1 to 6.0% by weight, preferably 0.2 to 4.0% by weight, calculated as SiO2 and referred to the total pigment.
7. Titanium dioxide pigment particles according to one or more of Claims 1 to 4,
characterised in that
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the content of doping elements of the dense skin is 0.01 to 3.0% by weight, preferably 0.05 to 2.0% by weight, calculated as oxide or in the case of F calculated as element and referred to the total pigment.
Titanium dioxide pigment particles according to Claim 5, characterised in that the aluminium content of the further layer is 0.5 to 6.0% by weight, preferably 1.0 to 4.0% by weight, calculated as AI2O3 and referred to the total pigment.
Method for manufacturing titanium dioxide pigment particles whose surface is coated with a dense SiO2 skin doped with at least one doping element, comprising the steps:
a) Reaction, in the gas phase, of titanium tetrachloride with an aluminium halide and a gas containing oxygen in a reactor at a temperature above 1,000 °C, in order to create a particle stream containing TiO2 particles,
b) Contacting of the particle stream with at least two oxide precursor compounds, where the first oxide precursor compound is a silicon compound and the second oxide precursor compound is selected from the group consisting of oxide precursor compounds of Sn, Sb, In, Y, Zn, Mn, Cu, Mo, Cd, Ce, W, Bi and precursor compounds of F, as well as mixtures thereof,
c) Cooling of the particle stream, in order to create pigment particles that are coated with a dense SiO2 skin doped with at least one doping element, where the doping elements are selected from the group Sn, Sb, In, Y, Zn, F, Mn, Cu, Mo, Cd, Ce, W and Bi, as well as mixtures thereof.
Method for manufacturing titanium dioxide pigment particles whose surface is coated with a dense SiO2 skin doped with at least one doping element, comprising the steps:
a) Provision of an aqueous suspension of TiO2 particles with a pH value in excess of 10,
b) Addition of an aqueous solution of an alkaline silicon component and at least one aqueous solution of a component containing a doping element, where the doping element is selected from the group Sb, In, Ge, Y, Nb, F, Mo, Ce, W and Bi, as well as mixtures thereof,
c) Deposition of a dense SiO2 skin doped with at least one doping element on the surface of the particles by lowering the pH value of the suspension to a value below 9, preferably to below 8, where the doping elements are selected from the group Sb, In, Ge, Y, Nb, F, Mo, Ce, W and Bi, as well as mixtures thereof.
Method according to Claim 9, characterised in that
a further layer of aluminium oxide is applied to the particle surface from the
gas phase.
Method according to Claim 9 or 10, characterised in that
a further layer of hydrous aluminium oxide is applied in a wet-chemical
process.
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13. Method according to Claim 9 or 10, characterised in that
the silicon content of the dense skin is 0.1 to 6.0% by weight, preferably 0.2 to 4.0% by weight, calculated as SiO2 and referred to the total pigment.
14. Method according to Claim 9 or 10, characterised in that
the content of doping elements of the dense skin is 0.01 to 3.0% by weight, preferably 0.05 to 2.0% by weight, calculated as oxide or in the case of F calculated as element and referred to the total pigment.
15. Method according to Claim 11 or 12, characterised in that
the aluminium content of the further layer is 0.5 to 6.0% by weight, preferably 1.0 to 4.0% by weight, calculated as AI2O3 and referred to the total pigment.
16. Method according to Claim 9,13 or 14, characterised in that
the compounds used as precursor compounds for SiO2 and for the oxides of the doping elements are the corresponding halides, particularly the corresponding chlorides.
17. Method according to Claim 11 or 12, characterised in that an organic coating is additionally applied.
18. Titanium dioxide pigment particles, manufactured according to one or more of Claims 9 to 17.
19. Use of the titanium dioxide pigmen particles according to one or more of Claims 1 to 8 or according to Claim 18 in plastics, paints, coatings, papers.
20. Use of the titanium dioxide pigment particles according to one or more of Claims 1 to 8 or according to Claim 18 as the starting basis for suspensions for producing paper or coatings.
21. Products comprising
titanium dioxide particles according to one or more of Claims 1 to 8 or according to Claim 18.
Dated this 24th day of June, 2008

HIRAL CHANDRAKANT JOSHI AGENT FOR KRONOS INTERNATIONAL, INC.
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Documents:

1349-MUMNP-2008-ABSTRACT(18-5-2010).pdf

1349-mumnp-2008-abstract(30-6-2008).pdf

1349-mumnp-2008-abstract(granted)-(11-4-2011).pdf

1349-mumnp-2008-abstract.doc

1349-mumnp-2008-abstract.pdf

1349-MUMNP-2008-CANCELLED PAGES(15-3-2011).pdf

1349-MUMNP-2008-CANCELLED PAGES(18-5-2010).pdf

1349-mumnp-2008-claims(30-6-2008).pdf

1349-MUMNP-2008-CLAIMS(AMENDED)-(15-3-2011).pdf

1349-MUMNP-2008-CLAIMS(AMENDED)-(18-5-2010).pdf

1349-mumnp-2008-claims(granted)-(11-4-2011).pdf

1349-mumnp-2008-claims.doc

1349-mumnp-2008-claims.pdf

1349-MUMNP-2008-CORRESPONDENCE(18-5-2010).pdf

1349-MUMNP-2008-CORRESPONDENCE(19-8-2008).pdf

1349-mumnp-2008-correspondence(ipo)-(12-4-2011).pdf

1349-mumnp-2008-correspondence.pdf

1349-mumnp-2008-description(complete)-(30-6-2008).pdf

1349-mumnp-2008-description(complete).doc

1349-mumnp-2008-description(complete).pdf

1349-mumnp-2008-description(granted)-(11-4-2011).pdf

1349-MUMNP-2008-DRAWING(18-5-2010).pdf

1349-mumnp-2008-drawing(30-6-2008).pdf

1349-mumnp-2008-drawing(granted)-(11-4-2011).pdf

1349-mumnp-2008-drawing.pdf

1349-mumnp-2008-english translation(30-6-2008).pdf

1349-MUMNP-2008-FORM 1(18-05-2010).pdf

1349-MUMNP-2008-FORM 1(19-08-2008).pdf

1349-mumnp-2008-form 1(30-6-2008).pdf

1349-mumnp-2008-form 1.pdf

1349-mumnp-2008-form 18.pdf

1349-mumnp-2008-form 2(complete)-(30-6-2008).pdf

1349-mumnp-2008-form 2(granted)-(11-4-2011).pdf

1349-MUMNP-2008-FORM 2(TITLE PAGE)-(18-5-2010).pdf

1349-mumnp-2008-form 2(title page)-(30-6-2008).pdf

1349-mumnp-2008-form 2(title page)-(granted)-(11-4-2011).pdf

1349-mumnp-2008-form 2(title page).pdf

1349-mumnp-2008-form 2.doc

1349-mumnp-2008-form 2.pdf

1349-MUMNP-2008-FORM 26(15-3-2011).pdf

1349-mumnp-2008-form 26(18-1-2011).pdf

1349-MUMNP-2008-FORM 3(18-5-2010).pdf

1349-mumnp-2008-form 3(30-6-2008).pdf

1349-mumnp-2008-form 3.pdf

1349-MUMNP-2008-FORM 5(18-5-2010).pdf

1349-mumnp-2008-form 5(30-6-2008).pdf

1349-mumnp-2008-form 5.pdf

1349-MUMNP-2008-FORM PCT-IB-373(18-5-2010).pdf

1349-MUMNP-2008-FORM PCT-ISA-237(18-5-2010).pdf

1349-mumnp-2008-form-pct-isa-210.pdf

1349-MUMNP-2008-PCT-OTHER(19-8-2008).pdf

1349-MUMNP-2008-PCT-RO-101(19-8-2008).pdf

1349-MUMNP-2008-PETITION UNDER RULE 137(18-5-2010).pdf

1349-mumnp-2008-power of attorney.pdf

1349-MUMNP-2008-REPLY TO EXAMINATION REPORT(18-5-2010).pdf

1349-MUMNP-2008-REPLY TO HEARING(15-3-2011).pdf

1349-MUMNP-2008-SPECIFICATION(AMENDED)-(18-5-2010).pdf

1349-mumnp-2008-wo-international publication report a2.pdf

1349-mumnp-2008-wo-international publication report a3.pdf


Patent Number 247482
Indian Patent Application Number 1349/MUMNP/2008
PG Journal Number 15/2011
Publication Date 15-Apr-2011
Grant Date 11-Apr-2011
Date of Filing 30-Jun-2008
Name of Patentee KRONOS INTERNATIONAL, INC.
Applicant Address POSTFACH 10 07 20, 51307 LEVERKUSEN,
Inventors:
# Inventor's Name Inventor's Address
1 DREWS-NICOLAI, LYDIA HOFRICHTERSTRASSE 3, 51057 KOELN,
2 BLUEMEL, SIEGFRIED AN DER DECKERSWEIDE 24, 40883 RATINGEN-EGGERSWCHEID,
PCT International Classification Number C09C1/36
PCT International Application Number PCT/EP2007/000762
PCT International Filing date 2007-01-30
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 102006004345.6 2006-01-30 Germany
2 102006054988.0 2006-11-22 Germany