AU2007209527A1

AU2007209527A1 - Titanium dioxide pigment featuring great opacity, and method for the production thereof

Info

Publication number: AU2007209527A1
Application number: AU2007209527A
Authority: AU
Inventors: Siegfried Bluemel; Lydia Drews-Nicolai; Volker Juergens; Volker Schmitt
Original assignee: Kronos International Inc
Current assignee: Kronos International Inc
Priority date: 2006-01-30
Filing date: 2007-01-25
Publication date: 2007-08-02
Anticipated expiration: 2027-01-25
Also published as: DE102006004344B4; TW200745274A; RU2480498C2; ES2394803T3; TWI417349B; SI1989264T1; DE102006004344A1; PL1989264T3; BRPI0706775B1; RU2008135143A; JP2009525367A; JP5237830B2; EP1989264B1; MY146261A; EP1989264A2; WO2007085445A3; KR101351817B1; CN101360793B; CN101360793A; UA95935C2

Description

CERTIFICATE OF VERIFICATION I, Michaela Kunigkeit of Bergerhof 69, 42799 Leichlingen, Germany state that to the best of my knowledge the attached document is true and complete translation of International PCT Application No. PCT/EP2007/000625 Date Signature of translator ,'u Ioi VV 1 l4 ' Titanium dioxide pigment of high opacity and method for its manufacture Field of the Invention 5 The invention relates to a titanium dioxide pigment of high opacity, a method for its manufacture and its use in decorative laminating papers or decorative foils. 10 Technological Background of the Invention Decorative laminating papers and decorative foils are part of a decorative, thermosetting coating material, used with preference for finishing furniture surfaces, for laminate flooring and in interior finishing. Laminates is the term used to denote materials in which, for example, 15 several impregnated, stacked layers of paper, or paper and hardboard or fibreboard, are pressed together. The use of special synthetic resins achieves extraordinarily high resistance of the laminates to marring, impact, chemicals and heat. The use of decorative laminating papers (which is always also intended to mean decorative foils 20 below) makes it possible to produce decorative surfaces, where the decorative laminating paper serves not only as facing paper, e.g. to hide unattractive wood material surfaces, but also as a carrier for the synthetic resin. The demands imposed on decorative laminating paper include, among others, opacity (hiding power), light-fastness (greying resistance), colour-fastness, wet strength, suitability for 25 impregnation and printability. The economic efficiency of the manufacturing process for decorative laminating papers is determined by, among other things, the opacity of the pigment in the paper. In principle, a pigment based on titanium dioxide is eminently suitable for achieving the necessary opacity of 30 the decorative laminating paper. During paper manufacture, a titanium dioxide pigment, or a titanium dioxide pigment suspension, is usually mixed with a pulp suspension. In addition to pigment and pulp as the feedstock, use is generally also made of auxiliaries, such as wet strength agents, and further additives where appropriate. The interactions of the individual components (pulp, pigment, auxiliaries and additives, water) with each other contribute to 35 formation of the paper and determine the retention of the pigment. Retention is the capacity for I U 101 VVU 2 of 14 retaining all inorganic substances in the paper during production. The surface charge of the pigment in relation to the pulp fibre plays an important role in this context. It is known that an improvement in opacity can be achieved by special treatment of the surface 5 of the titanium dioxide pigment. EP 0 713 904 B1 describes a surface treatment in which a first layer of aluminium oxide phosphate is applied at an acidic pH value of 4 to 6, and a second layer of aluminium oxide is precipitated in a pH range from 3 to 10, preferably at roughly pH 7. An improvement in retention 10 is achieved by a third layer consisting of magnesium oxide, the result being that the pigment produced is characterised by consecutive layers of aluminium oxide phosphate, aluminium oxide and magnesium oxide. DE 102 36 366 Al discloses a method for the surface treatment of a titanium dioxide pigment, in which a component containing phosphorus, titanium and aluminium is applied first by 15 precipitation, followed by a magnesium component at a pH value of 8 to 10. These pigments are said to display improved light-fastness and high opacity. DE 103 32 650 Al describes a method for the surface treatment of a titanium dioxide pigment, in which an aluminium component and a phosphorus component are added to the TiO 2 surface treatment suspension at a pH value of at least 10 and subsequently precipitated at a pH value 20 below 9. The method is said to lead to improved retention and unchanged opacity. US 6,200,375 discloses a weather-resistant titanium dioxide pigment for outdoor coatings, where the surface of the particles displays consecutive layers of zirconium hydroxide, titanium hydroxide, phosphate / silicon oxide and hydrous aluminium oxide. 25 Object and Summary of the Invention The object of the invention is to provide a titanium dioxide pigment for use in decorative laminating papers that has higher opacity compared to the prior art. The object of the invention 30 is additionally to provide a method for manufacturing a titanium dioxide pigment of this kind. The object is solved by a titanium dioxide pigment comprising coated rutile titanium dioxide particles, where the coating contains aluminium phosphate, aluminium oxide, titanium oxide and silicon oxide and where the specific surface to BET amounts to at least 15 m 2 /g. 35 The object is furthermore solved by a method for manufacturing a coated titanium dioxide pigment, comprising the steps I U 161 VVU 3 of 14 a) Provision of an aqueous suspension of uncoated titanium dioxide particles, b) Addition of an aluminium component and a phosphorus component, c) Addition of an alkaline silicon component and at least one pH-regulating component, where one of the pH-regulating components is an acid-reacting titanium component and where the pH 5 of the suspension is set to a value in the range from 4 to 9. Further advantageous versions of the invention are described in the sub-claims. 10 Description of the Invention Here and below, the term "oxide" is to be taken to also mean the corresponding hydrous oxides or the 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 15 the respective measuring accuracy known to the person skilled in the art. When used in the context of the present patent, the term "significant quantity" or "significant content" indicates the minimum quantity of a component, upwards of which the properties of the mixture are affected in the framework of the measuring accuracy. 20 The titanium dioxide pigment according to the invention is preferably a rutile titanium dioxide. It is characterised in that a layer of compounds containing aluminium/phosphorus/titanium/silicon is present on the particle surface. The silicon compound is silicon oxide and/or possibly silicon titanate. The combination of a silicon and a titanium component in Step c) of the method leads to precipitation in fluffy form, this resulting in an increase in the specific surface area to BET to 25 values of at least 15 m 2 /g, preferably 20 to 60 m 2 /g, particularly 20 to 35 m 2 /g, and improved opacity. The acid-reacting titanium component has an advantageous effect here. In the method according to the invention, a layer of compounds containing aluminium/ phosphorus/titanium/silicon is deposited on the titanium dioxide particle surface, referred to 30 below as the mixed layer for simplicity. An aluminium and a phosphorus component are first added to the TiO 2 suspension, in which context the pH value of the suspension can be in either the acidic or the alkaline range. Thereafter, an alkaline silicon component, an acid-reacting titanium component and, optionally, at least one other pH-regulating component are added to the suspension, either separately in any order or together, whereupon the pH value is in the 35 range from 4 to 9 and the mixed layer is deposited on the particle surface.

163 181 WO 4 of 14 The surface treatment method on which the invention is based starts with an aqueous, and preferably wet-milled, TiO 2 suspension (Step a)). Where appropriate, wet-milling is performed in the presence of a dispersant. The surface treatment does not take place during wet-milling. The TiO 2 comprises uncoated TiO 2 particles, i.e. TiO 2 base material particles, produced by the 5 sulphate process (SP) or the chloride process (CP). The base material is usually stabilised, by addition of aluminium at a rate of 0.3 to 3% by weight, calculated as A1 2 0 3 , and with an oxygen surplus of 2 to 15% in the gas phase during oxidation of the titanium tetrachloride into titanium dioxide in the CP process, and by doping with Al, Sb, Nb or Zn, for example, in the SP process. Rutile is used with preference, particularly produced by the chloride process. The surface 10 treatment method is preferably performed at a temperature of under 80 *C, particularly at 55 to 65 *C. The suspension in Step a) can be set to be either alkaline or acidic. In Step b), an aluminium and a phosphorus component are added. Suitable aluminium 15 components for the surface treatment method according to the invention are alkaline or acid reacting, water-soluble salts, e.g. sodium aluminate, aluminium sulphate, aluminium nitrate, aluminium chloride, aluminium acetate, etc. This selection is not to be interpreted as a restriction. The aluminium component is to be added in a quantity of 1.0 to 9.0% by weight, preferably 1.5 to 4.5% by weight, calculated as A1 2 0 3 and referred to the TiO 2 particle. 20 Suitable phosphorus components are inorganic compounds, such as alkali phosphates, ammonium phosphate, polyphosphates, phosphoric acid, etc. This selection is not to be interpreted as a restriction. Particularly suitable are disodium hydrogenphosphate or phosphoric acid. The phosphorus component is added in a concentration of 1.0 to 5.0% by weight, preferably 1.5 to 4.0% by weight, calculated as P 2 0 5 and referred to the TiO 2 particle. 25 In Step c), an alkaline silicon component, an acid-reacting titanium component and, optionally, one or more other pH-regulating components are added, such that a pH value in the range from 4 to 9, preferably in the range from 4 to 6, and particularly a pH value of roughly 5, is obtained. The alkaline silicon component is preferably sodium or potassium waterglass. Between 0.1 and 30 5.0% by weight, preferably 1.0 to 3.0% by weight, Si0 2 are added, referred to the uncoated TiO 2 particle. The acidic titanium component is preferably titanium oxide chloride or titanium oxide sulphate. Between 0.1 and 6.0% by weight of the titanium component are added, calculated as TiO 2 and referred to the uncoated TiO 2 particle. 35 The pH-regulating component used can be an acid or a lye. Examples of the acid that can be used are sulphuric acid, hydrochloric acid, phosphoric acid or another suitable acid. Moreover, a 1I U161 WU b o 14 corresponding, acid-reacting salt, such as aluminium sulphate, can also be used in place of the acid. Sodium hydroxide solution is preferably used as the lye. Alkaline-reacting salts are also suitable. The person skilled in the art is familiar with suitable pH-regulating compounds. The selection is thus not to be interpreted as a restriction of the invention. 5 It has proven advantageous to apply, in a subsequent Step d), a layer of aluminium oxide to the mixed layer in such a way that the pH value is maintained in the range from 4 to 9 by parallel addition of an alkaline and an acidic component (e.g. sodium aluminate / aluminium sulphate), or by addition of an alkaline aluminium component, such as sodium aluminate, and an acid, e.g. 10 sulphuric acid or hydrochloric acid, or by addition of an acidic aluminium component, such as aluminium sulphate, together with a lye, e.g. NaOH. In this context, either the components can be added in such a way that the pH value remains constant at a value in the range from 4 to 9, or the components can be added in such a combination that the pH value varies within the pH value range from 4 to 9 during addition. The person skilled in the art is familiar with these 15 procedures. Suitable for setting the pH value are, for example, lyes or acids (e.g. NaOH /

H

2 SO4), or alkaline or acid-reacting salt solutions (e.g. sodium aluminate / aluminium sulphate). It has proven particularly advantageous to perform treatment at the pH value previously set in Step c). 20 As and when required, the pH value is set to roughly 6 to 7 in a final Step e), e.g. using lyes / acids (e.g. NaOH / H 2

SO

4 ) or with alkaline / acidic salt solutions, such as sodium aluminate / aluminium sulphate. The quantity of the aluminium components used in Steps c), d) and e), calculated as A1 2 0 3 , is to be added to the quantity of A1 2 0 3 previously used in Step b). The sum total of the aluminium 25 components used in Steps b) to e), calculated as A1 2 0 3 and referred to the uncoated TiO 2 particle, is ideally 1.0 to 9.0% by weight, preferably 2.0 to 8.0% by weight, and particularly 3.0 to 6.5% by weight. Similarly, the quantity of the phosphorus component possibly used in Steps c) and d), calculated as P 2 0 5 , is to be added to the quantity of P 2 0 5 used in Step b). The sum total of the phosphorus components used in Steps b) to d), calculated as P 2 0 5 , is ideally 1.0 to 5.0% 30 by weight, preferably 1.5 to 4.0% by weight, calculated as P 2 0 5 and referred to the uncoated TiO 2 particle. In a special embodiment of the method according to the invention no significant quantities of a Zr or a Ce component are used. 35 As a rule, it is not necessary to finally subject the surface-treated pigment to heat treatment at temperatures > 200 *C.

TG 181 WO 6 of 14 In a preferred embodiment of the method according to the invention, the starting point is an alkaline TiO 2 suspension. To this end, Step a) first involves setting the suspension to a pH value of at least 10 using suitable alkaline compounds, e.g. NaOH. If wet-milling is performed, this 5 should ideally be done before the milling operation. In Step b), an aluminium and a phosphorus component are then added to the suspension, each in the form of an aqueous solution. During addition of the components, the pH of the suspension is maintained at a value of at least 10, preferably at least 10.5, and particularly preferably at least 11. 10 Sodium aluminate is particularly suitable as the alkaline aluminium component. If an acid reacting compound is used, such as aluminium sulphate, the addition of which would reduce the pH value to below 10, it has proven advantageous to compensate for this effect by adding a suitable alkaline compound, such as NaOH. The person skilled in the art is familiar with suitable alkaline compounds and the quantities required for maintaining the pH at a value of at least 10. 15 In the case of phosphorus components whose addition would reduce the pH value to below 10, it has likewise proven advantageous to compensate for this effect by adding a suitable alkaline compound, such as NaOH. The person skilled in the art is familiar with suitable alkaline compounds and the quantities required for maintaining the pH at a value of at least 10. The Al and the P component can be added to the suspension in any order, individually one after 20 the other, or simultaneously. In Step c), there then follows the addition of an alkaline silicon component, the addition of an acid-reacting titanium component and, where appropriate, the optional addition of at least one other pH-regulating component, in order to set the pH to a value in the range from 4 to 9. The silicon component, the acid-reacting titanium component and the other pH-regulating 25 component(s) can be added either consecutively or simultaneously, and also in several stages and in any order. The alkaline silicon component is preferably sodium or potassium waterglass. The titanium component is preferably titanium oxide chloride. The additionally used acid reacting component is preferably hydrochloric acid. 30 In an alternative embodiment of the method according to the invention, the surface treatment according to the invention is started in the acidic pH range. In this case, Step b) involves the addition of such aluminium and phosphorus components that the pH value of the suspension is subsequently below 4. The person skilled in the art is at 35 liberty to already reduce the pH value in Step a) by means of a suitable acid, or to reduce the pH value to below 4 in Step b) using a suitable combination of the components, and adding an I k3 1 VV U ( of 14 acid where appropriate. For example, the combination phosphoric acid / sodium aluminate or disodium hydrogenphosphate I aluminium sulphate is suitable. The components can be added to the suspension in any order, individually one after the other, or simultaneously. In Step c), the alkaline silicon component, preferably sodium or potassium waterglass, and the 5 acid-reacting titanium component, preferably titanium oxide chloride, are added. The addition of a further pH-regulating component may possibly be necessary, in order to set the pH to a value in the range from 4 to 9. The components can be added in Step c) either consecutively or simultaneously, and also in several stages and in any order. Depending on the quantity, nature and order of the components added in Step c), the pH value of the suspension can briefly rise to 10 values over 9 in the course of the individual additions. The surface-treated TiO 2 pigment is separated from the suspension by filtration methods known to the person skilled in the art, and the resultant filter cake is washed in order to remove the soluble salts. To improve the light-fastness of the pigment in the laminate, a nitrate-containing 15 compound, e.g. KNO 3 , NaNO 3 , Al(N0 3

)

3 , can be added to the washed filter paste in a quantity of 0.05 to 1.0% by weight, calculated as NO 3 , before or during subsequent drying. During subsequent milling, e.g. in a steam mill, an organic compound can be added to the pigment, taken from the range customarily used in the manufacture of TiO 2 pigments and familiar to the person skilled in the art, such as polyalcohols (trimethylolpropane). As an alternative to addition 20 of the nitrate-containing compounds before or during drying, such substances can also be added during milling. Compared to the reference pigments, the pigment manufactured according to this method displays improved opacity and is optimally suited to use in decorative laminating paper. 25 Moreover, the titanium dioxide pigment according to the invention is characterised by the fact that the position of the isoelectric point (IEP) can be set via the quantity of precipitated TiO 2 or SiO2 in Step c) and A1 2 0 3 in Step d). The IEP characterises the pH value of the aqueous pigment suspension at which the pigment surface charge approaches zero. The surface charge of the pigment according to the invention can thus be shifted into the positive or negative range, 30 depending on the requirements of the paper manufacturing process. The surface treatment method according to the invention is customarily performed in batch mode. It is, however, also possible to perform treatment continuously, in which case suitable mixing equipment, such as is familiar to the person skilled in the art, must guarantee sufficiently 35 thorough mixing.

I l 1W1 VVU 8 of 14 Examples Examples of the invention are described below, yet these examples are not intented to restrict the scope of the invention. 5 Example 1 A sand-milled rutile TiO 2 suspension from the chloride process with a TiO 2 concentration of 350 g/I was set to a pH value of 10 with NaOH at 60 'C. While stirring, 3.5% by weight A1 2 0 3 10 were added to the suspension in the form of sodium aluminate. After stirring for 10 minutes, 2.4% by weight P 2 0 5 were added in the form of disodium hydrogenphosphate solution. This was followed by stirring for a further 10 minutes. In the next step, the suspension was set to a pH value of 5 by adding titanium oxide chloride (corresponding to 3.0% by weight TiO 2 ) and 2.4% by weight SiO 2 in the form of sodium waterglass. In this context, the SiO 2 was added in 2 steps, 15 each with 1.2% by weight SiO 2 , at a pH value of 10.5 and of 7, parallel to the addition of the titanium oxide chloride. After stirring for 10 minutes, 1.9% by weight A1 2 0 3 were subsequently added in the form of parallel addition of sodium aluminate solution and HCI, such that the pH value was maintained at 5. After stirring for 30 minutes, the suspension was set to a pH value of approx. 5.8 with the help 20 of an alkaline sodium aluminate solution, filtered and freed of the water-soluble salts by washing. The washed filter paste was dried in the plate drier and subsequently steam-milled. The pigment displayed a BET value of 32 m 2 /g, the isoelectric point being at a pH value of 5.2. During preparation of the handsheets, the zeta potential of the diluted stock suspension was set to a value of +16 mV or -12 mV by adding wet-strength agent. 25 Example 2 A sand-milled rutile TiO 2 suspension from the chloride process with a TiO 2 concentration of 30 350 g/I was set to a pH value of 10 with NaOH at 60 *C. While stirring, 3.5% by weight A1 2 0 3 were added to the suspension in the form of sodium aluminate. After stirring for 10 minutes, 2.4% by weight P 2 0 5 were added in the form of disodium hydrogenphosphate solution. This was followed by stirring for a further 10 minutes. In the next step, the suspension was set to a pH value of 5 by adding titanium oxide chloride (corresponding to 2.8% by weight TiO 2 ). Next, 1.2% 35 by weight SiO 2 were added in the form of sodium waterglass. After stirring for 10 minutes, the pH value was set to 5 with HCI. Subsequently, 1.9% by weight A1 2 0 3 were added in the form of 1%0 vv jOT 14 parallel addition of sodium aluminate solution and HCI, such that the pH value was maintained at 5. After stirring for 30 minutes, the suspension was set to a pH value of approx. 5.8 with the help of an alkaline sodium aluminate solution, filtered and freed of the water-soluble salts by 5 washing. The washed filter paste was dried in the plate drier and subsequently steam-milled. The pigment displayed a BET value of 26 m 2 /g, the isoelectric point being at a pH value of 6.0. During preparation of the handsheets, the zeta potential of the diluted stock suspension was set to a value of +18 mV or -14 mV by adding wet-strength agent. 10 Example 3 Same as Example 2, but the sodium waterglass (corresponding to 2.4% by weight SiO 2 ) was added to the suspension before the titanium oxide chloride solution (corresponding to 3.0% by 15 weight TiO 2 ). The pigment displayed a BET value of 30 m 2 /g, the isoelectric point being at a pH value of 5.9. During preparation of the handsheets, the zeta potential of the diluted stock suspension was set to a value of +12 mV or -16 mV by adding wet-strength agent. 20 Example 4 Same as Example 3, but 1.2% by weight SiO 2 and 2.9% by weight TiO 2 were used. The pigment displayed a BET value of 27 m 2 /g, the isoelectric point being at a pH value of 6.2. 25 Example 5 Same as Example 3, but 0.6% by weight SiO 2 and 2.9% by weight TiO 2 were used. 30 The pigment displayed a BET value of 26 m 2 /g, the isoelectric point being at a pH value of 6.4. Reference example 1 35 A sand-milled rutile TiO 2 suspension from the chloride process with a TiO 2 concentration of 350 g/l was set to a pH value of 10 with NaOH at 60 *C. While stirring, 2.0% by weight A1 2 0 3 II. IZ1 wU 10 of 14 were added to the suspension in the form of sodium aluminate solution. After stirring for 10 minutes, 2.4% by weight P 2 0 5 were added to the suspension in the form of disodium hydrogen phosphate solution. Stirring for 10 minutes then followed. In the next step, the suspension was set to a pH value of 5 by adding aluminium sulphate solution (corresponding to 2.6% by weight 5 A1 2 0 3 ). Subsequently, 0.8% by weight A1 2 0 3 was added in the form of parallel addition of aluminium sulphate and sodium aluminate, such that the pH value was maintained at 5. After stirring for 30 minutes, the acidic suspension was set to a pH value of approx. 5.8 with the help of an alkaline sodium aluminate solution, filtered and freed of the water-soluble salts by washing. The washed filter paste was dried in a plate drier and subsequently steam-milled. 10 The pigment displayed a BET value of 12 m 2 /g. During preparation of the handsheets, the zeta potential of the diluted stock suspension was set to a value of +16 mV in each case by adding wet-strength agent. Setting a negative zeta potential resulted in insufficient wet strength of the paper. 15 Reference example 2 A sand-milled rutile TiO 2 suspension from the chloride process with a TiO 2 concentration of 350 g/l was set to a pH value of 10 with NaOH at 60 *C. While stirring, 2.0% by weight A1 2 0 3 was added to the suspension in the form of sodium aluminate solution. After stirring for 10 20 minutes, 2.4% by weight P 2 0 5 were added to the suspension in the form of disodium hydrogen phosphate solution. Stirring for 10 minutes then followed. 1.0% by weight Si0 2 in the form of sodium waterglass was added to the suspension. In the next step, the suspension was set to a pH value of 5 by adding aluminium sulphate solution (corresponding to 2.7% by weight A1 2 0 3 ). Subsequently, 0.8% by weight A1 2 0 3 was added in the form of parallel addition of aluminium 25 sulphate and sodium aluminate, such that the pH value was maintained at 5. After stirring for 30 minutes, the acidic suspension was set to a pH value of approx. 5.8 with the help of an alkaline sodium aluminate solution, filtered and freed of the water-soluble salts by washing. The washed filter paste was dried in a plate drier and subsequently steam-milled. The pigment displayed a BET value of 12 m 2 /g. 30 Test methods For assessing the optical properties of the decorative laminating papers, and thus the quality of 35 the titanium dioxide pigment, it is important to compare decorative laminating papers with an 1%u Iu I v llj Ot 14 identical ash content. Sheets of decorative laminating paper with a sheet weight of roughly 80 g/m 2 and an ash content of roughly 30 g/m 2 were produced. The sheets of decorative laminating paper were produced by two different methods in parallel. In the "one-step method", the pigment to be tested was simultaneously dispersed with pulp and 5 commercially available wet-strength agent in water to produce the sheets. This was followed by the sheet-forming operation. The person skilled in the art is familiar with the procedure. Wet strength agent was added until the zeta potential of the diluted stock suspension, measured with a Mjtek SZP 06 system zeta potential measuring instrument, was in the range from +10 mV to +20 mV. 10 In the "split method", the pulp and a previously determined quantity of wet-strength agent were first beaten in water. Only after a retention time was the pigment to be tested added and dispersed. This was followed by the sheet-forming operation. The person skilled in the art is familiar with the procedure. The necessary quantity of wet-strength agent was determined in a separate test with the help of 15 the zeta potential of the diluted stock suspension. A given quantity of pulp and titanium dioxide pigment was beaten in water to this end. Wet-strength agent was subsequently added until the zeta potential of the diluted stock suspension was in the range from -10 mV to -20 mV. The quantity of wet-strength agent used for both methods was of the customary order of magnitude of 1 to 4% by weight wet-strength agent (active substance), referred to pulp (oven-dry). 20 The titanium dioxide content (ash) of a sheet and the pigment retention were subsequently determined. a) Ash content 25 The titanium dioxide content was determined by incinerating a defined weight of the produced paper in a rapid incinerator at 900 "C. The TiO 2 content by mass (ash) in % by weight was obtained by weighing the residue. The following formula was used as the basis for calculating the ash content: Ash content [g/m 2 ] = (Ash [% by weight] x Grammage [g/m 2 ]) / 100 [%]. 30 b) Optical properties The optical properties of the pigments were determined in laminates. To this end, the decorative laminating paper was impregnated with a modified melamine impregnating resin and pressed into laminates. The sheet to be impregnated with resin was 35 completely immersed in the melamine resin solution, subsequently drawn between 2 doctor blades to ensure application of a specific amount of resin and then immediately pre-condensed 1% 101 VVU 12 Of 14 at 130 *C in a recirculating-air drying oven. The amount of resin applied was 120 to 140% of the weight of the sheet. The sheet had a residual moisture content of approx. 6% by weight. The condensed sheets were combined into books with phenolic resin-impregnated core papers and white/black underlay paper. 5 The laminate structure used for assessing the test pigments comprised 11 layers: decorative laminating paper, white/black underlay, core paper, core paper, core paper, white underlay, core paper, core paper, core paper, white/black underlay, decorative laminating paper. The books were pressed for 300 seconds with the help of a Wickert Type 2742 laminating press at a temperature of 140 "C and a pressure of 900 N/cm 2 . 10 The optical properties of the laminates were measured using a commercially available spectrophotometer. In order to assess the optical properties of the laminates, the optical values of the decorative laminating papers (CIELAB L*, a*, b*) to DIN 6174 were determined with the help of the ELREPHO* 3000 colorimeter over white and black underlay. The opacity is a measure of the 15 light transmission of the paper. The following parameters were selected as a measure of the opacity of the laminates: CIELAB L*biack, the brightness of the laminates measured over black underlay paper, and the opacity value L [%] = Yback/Nwhite X 100, determined from the Y-value of the decorative laminating papers measured over black underlay paper (YbIaca) and the Y-value measured over white underlay paper (Ywtite). 20 c) Specific surface area to BET (Brunauer-Emmett-Teller) The BET surface was measured according to the static volumetric principle, using a Tristar 3000 from Micromeritics. 25 d) Isoelectric point The measuring method is based on determination of the electrophoretic mobility of the pigment particles in an electrolyte solution upon application of an electrical field. The pigment to be tested was dispersed in 0.01 M aqueous KCI solution. The profile of the zeta potential of the specimen as a function of the pH value was subsequently determined using a Zetasizer 3000 30 HSA from Malvern. The isoelectric point characterises the pH value at which the zeta potential is zero. 35 TG 181 WO 13 of 14 Test results Pigment BET Opacity (+) Opacity (-) [m 2 /g] L*biack L %] L*black L [o] 5 ---------- ------ ---------------------------------------------------------------------------------------- Example 1 32 90.7 91.9 90.8 92.2 Example 2 26 90.4 91.5 90.8 92.3 Example 3 30 90.5 91.6 90.9 92.2 Reference 1 12 90.2 91.0 - 10 Reference 2 12 90.3 91.0 n.d. n.d. (+) Zeta potential of the diluted stock suspension set to a positive value (-) Zeta potential of the diluted stock suspension set to a negative value 15 - Sufficent wet-strength of the paper not achievable n.d. not determined Example pigments 1, 2 and 3 according to the invention demonstrate improved opacity and higher BET values compared to the reference pigments 1 and 2. 20 Example pigments 1 and 2, or 3, 4 and 5, moreover demonstrate that an increasing SiO 2 content in the coating shifts the isoelectric point (IEP) towards lower pH values. In contrast to the reference pigment 1, both a positive and a negative zeta potential can be set when using the example pigments and adding customary quantities of wet-strength agent.

Claims

1. Titanium dioxide pigment containing coated rutile titanium dioxide particles, where the coating contains aluminium phosphate, aluminium oxide, titanium oxide and silicon oxide and where the specific surface to BET amounts to at least 15 m 2 /g.

2. Titanium dioxide pigment according to Claim 1, characterised in that the aluminium content of the coating is 1.0 to 9.0% by weight, preferably 2.0 to 8.0% by weight, and particularly 3.0 to 6.5% by weight, calculated as A1 2 0 3 .

3. Titanium dioxide pigment according to Claim 1 or 2, characterised in that the phosphorus content of the coating is 1.0 to 5.0% by weight, preferably 1.5 to 4.0% by weight, calculated as P 2 0 5 .

4. Titanium dioxide pigment according to one or more of Claims 1 to 3, characterised in that the silicon content of the coating is 0.1 to 5.0% by weight, preferably 1.0 to 3.0% by weight, calculated as SiC2

5. Titanium dioxide pigment according to one or more of Claims 1 to 4, characterised in that the titanium content of the coating is 0.1 to 6.0% by weight, calculated as TiC 2 .

6. Titanium dioxide pigment according to one or more of Claims 1 to 5, characterised in that the specific surface area to BET is 20 to 60 m 2 /g, preferably 20 to 35 m 2 /g.

7. Method for manufacturing a coated titanium dioxide pigment, comprising the steps a) Provision of an aqueous suspension of uncoated titanium dioxide particles, b) Addition of an aluminium component and a phosphorus component, c) Addition of an alkaline silicon component and at least one pH-regulating component, where one of the pH-regulating components is an acid-reacting titanium component and where the pH of the suspension is set to a value in the range from 4 to 9. I U 161 WVU 2 Ot j

8. Method according to Claim 7, characterised by the steps: a) Provision of an aqueous suspension of uncoated titanium dioxide particles, where the pH value is at least 10, b) Addition of an aluminium component and a phosphorus component, where the pH of the suspension is maintained at a value of at least 10, c) Addition of an alkaline silicon component and at least one pH-regulating component, where one of the pH-regulating components is an acid-reacting titanium component and where the pH of the suspension is set to a value in the range from 4 to 9.

9. Method according to Claim 7 or 8, characterised in that, following Step c), an aluminium oxide layer is applied in a Step d), maintaining the pH value of the suspension in the range from 4 to 9, by adding an alkaline aluminium component and an acidic aluminium component or an acid.

10. Method according to one or more of Claims 7 to 9, characterised in that, in a final Step e), the final pH value of the suspension is set to roughly 6 to 7 with the help of a lye / acid, or with an alkaline / acidic salt solution.

11. Method according to one or more of Claims 7 to 10, characterised in that the sum total of the aluminium components added in Steps b) to e) is 1.0 to 9.0% by weight, preferably 2.0 to 8.0% by weight, and particularly 3.0 to 6.5% by weight, calculated as A1 2 0 3 .

12. Method according to one or more of Claims 7 to 11, characterised in that the sum total of the phosphorus components added in Steps b) to e) is 1.0 to 5.0% by weight, preferably 1.5 to 4.0% by weight, calculated as P 2 0 5 .

13. Method according to one or more of Claims 7 to 12, characterised in that the quantity of silicon component added in Step c) is 0.1 to 5.0% by weight, preferably 1.0 to 3.0% by weight, calculated as SiO 2 .

14. Method according to one or more of Claims 7 to 13, characterised in that the quantity of titanium component added in Step c) is 0.1 to 6.0% by weight, calculated as TiO 2 . 1) UI s)

15. Method according to one or more of Claims 1 to 14, characterised in that the pigment is treated with nitrate, such that the finished pigment contains 0.05 to 1.0% by weight NO 3 .

16. Method according to one or more of Claims 1 to 15, characterised in that an organic compound is applied during final milling.

17. Titanium dioxide pigment manufactured by a method according to one or more of Claims 7 to 16.

18. Use of the titanium dioxide pigment according to Claim 1 or 17 in the manufacture of decorative laminating paper.

19. Decorative laminating paper containing a titanium dioxide pigment according to Claim 1 or 17.

20. Use of decorative laminating paper containing a titanium dioxide pigment according to Claim 1 or 17 for the manufacture of decorative coating materials.

21. Decorative coating material containing decorative laminating paper according to Claim 19.

22. Laminate containing decorative laminating paper according to Claim 19.