Patent Application
20070298059
The invention involves the addition of a marker substance, which can be used to identify the product, to the titanium dioxide pigment during the manufacturing of the product. The terms “product” and “end product” are used equivalently below. The invention encompasses the use of both one marker substance and several marker substances in pigment production.
As is generally known, titanium dioxide pigment is produced from iron-titanium ores, iron-titanium slags or corresponding heavy-mineral concentrates by the so-called sulphate process or the so-called chloride process. The pure titanium dioxide, also referred to as titanium dioxide base material, is conditioned with the help of certain additives in such a way that the pigmentary optical properties, e.g. brightness, tinting strength and tone, and also the photostability and the processing properties (flow properties, dispersion performance, etc.), are optimised for the respective application. Conditioning is performed by doping with suitable elements in the crystal lattice and/or by coating the surface with suitable inorganic and/or organic compounds.
A dense SiO2 coating, for example, leads to improved photostability of the TiO2 pigment. The pigment dispersibility in aqueous systems is, on the other hand, improved by final coating with a layer of hydrous aluminium oxide. The TiO2 pigment is surface-treated with silanes for easier incorporation in plastics. These methods are exhaustively described in the prior art (e.g. Ullmann's Encyclopedia of Industrial Chemistry, CD-ROM 2006, 7th Edition: “Inorganic Pigments, Chapter 2.1.3.4. Aftertreatment”) and well known to the person skilled in the art.
The impact of the additives on the physico-chemical behaviour, and thus the utility of the titanium dioxide pigment in its customary fields of application (paints and coatings, plastics, fibres, paper, etc.) is likewise known. It is therefore desirable that the marker substances used in the present invention do not alter the properties of the titanium dioxide pigment optimised for the intended field of application, but can nevertheless be detected in the end product with the help of suitable methods. Similarly, it is desirable that no negative effects on the properties of the end product occur, e.g. due to interactions with other raw material components.
It is desirable that the detection methods to be used for the marker substances yield unequivocal, reconstructable results. Examples of suitable methods include X-ray fluorescence analysis (XRF), atomic absorption spectroscopy (MS), atomic emission spectroscopy (flame AES, ICP-AES), neutron activation analysis (NM) and ICP mass spectrometry (ICP-MS).
The marker substance to be used according to the invention can be added both by doping in the crystal lattice and when coating the surface (hereafter: surface treatment). Marking during surface treatment is preferred for reasons of process engineering.
Different marker substances can be used in combination. Defined concentration ratios can be set in this context, such that the product is virtually identified by a marker substance code. Individual production batches can be distinguished from each other in this way. The combination of two or more marker substances leads to improved unequivocalness of identification and less risk of confusion of marked and unmarked products.
Suitable marker substances are, in principle, all elements that are not used anyway for the doping or surface treatment of the pigment, or are not present in the TiO2 as detectable contamination—originating from the ore or the slag, such as Cr, V or Nb—or do not occur as impurities or components in the end product. It is desirable that the marker substances not contain any colouring elements.
As the marker substances are at all events used in minimal concentrations, colouring elements can be used in cases where whiteness plays no decisive role in the end product.
Particularly suitable as marker substances are the rare-earth metals (lanthanides), yttrium, zinc, molybdenum, tungsten, germanium, tin and scandium.
One or more marker substances can be used.
The marker substances can be added at various points of the TiO2 production process. It is preferable that the marker substance be bound so firmly to the TiO2 surface that it is not detached by washing or other subsequent processing steps, and that it be uniformly distributed in the pigment volume.
In one embodiment of the invention, the marker substance(s) is/are added prior to calcining in the framework of the sulphate process.
The method for adding the marker substances preferably fits in with the surface treatment method used in the specific case. Aqueous surface treatment customarily starts with an aqueous titanium dioxide base material suspension, which is first milled in a stirred mill and to which the solution of a corresponding water-soluble salt of the coating substance is then added, e.g. the corresponding sulphate, nitrate, phosphate or chloride, etc. As a result of appropriate pH value control, a hydrated oxide or a phosphate is deposited on the titanium dioxide surface. The pigment is subsequently separated by filtration, freed of water-soluble salts by washing, dried and steam-milled. In this method, the marker substance can be added to the suspension as an appropriate quantity of a water-soluble compound and precipitated at a given pH value. It is likewise possible to add the marker substance during steam milling or during drying. Similarly, one or several different marker substances can be added at different points of the TiO2 production process. Moreover, the marker substance can also be added as an atomised suspension, or dissolved in an organic solvent, e.g. together with silicone oil treatment in the steam mill.
Surface treatment of titanium dioxide base material in the gas phase is usually performed directly following formation of the TiO2 base material particles from a gas containing TiCl4 and oxygen, at temperatures customarily exceeding 800° C. The coating substance is fed into the reactor as a gaseous compound at a point where the TiO2 formation reaction has almost been completed. It forms a uniform oxide skin on the particle surface. These surface treatment methods are described in, for example, WO 96/36441, EP 0 767 759 B1 and WO 01/81480 A2. The TiO2 particles are subsequently cooled, separated from the gaseous suspension, additionally subjected to aqueous surface treatment where appropriate, dried and finally steam-milled. For addition of the marker substance during surface treatment in the gas phase, use is preferably made, according to the invention, of a compound of the marker substance that is gaseous at temperatures >800° C., e.g. the corresponding halide. The compound of the marker substance is fed into the reactor together with, or in the direct vicinity of, the other coating substances and is likewise precipitated on the particle surface in the form of an oxide. It is likewise possible to add the marker substance during steam milling or during drying. Similarly, one or several different marker substances can be added at different steps in the process.
The marker substance can also be used as the sole surface treatment component. In this case, the marker substance(s) is/are preferably added during steam milling and/or during drying and/or during calcining in the case of the sulphate process.
The concentration of the marker substance used is preferably minimised, for cost reasons and in order to make detection more difficult for third parties. Detection is dependent on the actual concentration of the substance in the end product and on the detection limit of the detection method to be used. The marker substance is preferably present in a concentration of up to 1% by weight, particularly 0.005 to 0.1% by weight, particularly preferably 0.01 to 0.1% by weight, referred to TiO2.
In order to be able to achieve reliable, reproducible analysis results, the person skilled in the art will target a minimum concentration corresponding to the detection limit of the substance in question in the sample to be analysed. As the pigment is usually only present in the end product in low concentrations of a few percent, it is in most cases necessary to increase the concentration of the sample of the end product to be analysed in terms of TiO2 and marker substance. Application
The method according to the invention, for identifying and verifying of products containing titanium dioxide pigment particles, is suitable for use in, for example, the fields of fibres for textiles, papers for documents and currency, in the pharmaceutical sector, and also for plastics, paints and coatings.
In the textile fibres sector, marked TiO2 pigments can, for example, be used to mark special, high-quality fibres, and the products made of them, and protect them against imitation. In addition, manufacturers of high-quality, branded garments can identify fakes by using fibre fabrics delustered with correspondingly marked TiO2 pigments in their products. As a fibre delustering agent, TiO2 is usually used in the range of 0.3 to 1% by weight. If the pigment is coated with roughly 100 ppm to 1,000 ppm marker substance, the latter is contained in the fibre in a concentration of 0.3 ppm to 10 ppm.
High-quality papers contain TiO2 pigment in the pulp or in the coating, usually in a concentration of up to 10% by weight. Marked TiO2 pigment can be used in the production of special papers, e.g. for identity cards, certificates or bank notes, on the one hand in order to identify forgeries and, on the other hand, to track the distribution channels of the papers—even of individual batches—for example.
TiO2 pigment is also used in pharmaceuticals, as a brightener in tablets or for pigmenting the surface coating of medications in the form of coated tablets, usually in quantities of up to roughly 3% by weight, referred to the coating. With the help of the marking according to the invention, fakes can be distinguished from the original pharmaceuticals, and it is furthermore again possible to track the distribution channels, even of individual production batches.
In the plastics sector, the marking of the TiO2 pigment can help the pigment manufacturer to distinguish between its own pigments and third-party pigments in the plastic end product, and to defend itself against unjustified compensation claims in connection with complaints, e.g. relating to discolouration of PVC window profiles.
In the field of paints and coatings, too, e.g. in vehicle refinish paints or other high-quality coatings, the pigment manufacturer can identify its own and third-party pigments with the help of the pigment marking.
The method according to the invention for marking titanium dioxide pigment particles offers the following advantages:
Use of the marking method presents no problems, since no additional process steps or equipment are necessary during TiO2 production other than the steps according to the present invention.
Methods for detecting the marker substances of the present invention are established.
The additional costs for TiO2 production are low.
The present invention also includes a method involving testing a product to determine whether it contains the titanium dioxide pigment particles produced by the method of this invention. In addition, the step of assessing the test results from the test can be used to determine whether the product is the product containing the titanium dioxide pigment particles produced by the method of this invention. Thus, the methods of this invention can be used to verify authentic product and to identify product forgeries (product piracy), to track distribution channels, or to identify the pigment used in order to counter unjustified complaints. One such method for marking titanium dioxide pigment particles and for verifying marked titanium dioxide pigment particles includes the steps of: using a quantity of at least one marker substance during production of the titanium dioxide particles, wherein the marker substance is detectable in a product containing the titanium dioxide particles; recording information about the marker substance; testing a product to determine whether it contains the marker substance; and comparing the results of the test to the recorded information to determine whether the product contains the marker that was used during the production of the titanium dioxide particles.
The invention is explained in detail on the basis of the example below, without this in any way restricting the invention.
A suspension of dry-milled anatase produced by the sulphate process, with a TiO2 concentration of 500 g/l, is mixed at 60° C. with 0.1% sodium hexametaphosphate as dispersant and set to a pH value of 10 with NaOH. While stirring, 1.0% by weight SiO2, referred to TiO2, is added to the suspension in the form of sodium waterglass. HCl is then used to set the pH value to 7. While stirring, 300 ppm La2O3, referred to TiO2, are next added to the suspension in the form of lanthanum sulphate, and the pH value is again set to 7 with NaOH or HCl. Subsequently, 2.0% by weight Al2O3, referred to TiO2—added in the form of sodium aluminate—is precipitated onto the pigment particles at a pH value of 6.5 to 7.5 by means of a fixed-pH method using HCl.
The suspension is set to a pH value of 6.8, freed of water-soluble salts by washing, and dried. Treatment with silicone oil is performed during final steam-milling.
The TiO2 pigment marked with lanthanum oxide is used for delustering polyester fibres in a concentration of 0.5% by weight TiO2. A TiO2 suspension in ethylene glycol is used in this context. The ethylene glycol is reacted with dimethyl terephthalate, the methanol formed is distilled off, and the liquid polyester is withdrawn from the reaction vessel. Filaments with a fibre diameter of a few μm are produced from the delustered polyester strands in further processing steps, and further intermediate steps, such as spinning, weaving, etc., are performed to produce a polyester fabric, e.g. for high-quality textiles, such as net curtains.
To analyse the marker substance in the polyester fibre, 10 g polyester fibre are incinerated at roughly 800° C. The residue is decomposed in a potassium carbonate melt, and the melt dissolved in hydrochloric acid after cooling. The lanthanum is measured by ICP-AES at a wavelength of 408.672 nm, and the concentration determined via a calibration function. The La2O3 concentration is 1.5 ppm, referred to the polyester fibre.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 029 284 | Jun 2006 | DE | national |
This application claims the benefit of U.S. Provisional patent application Ser. No. 60/807,293 filed Jul. 13, 2006 and the benefit of DE 10 2006 029 284 filed Jun. 23, 2006.
| Number | Date | Country | |
|---|---|---|---|
| 60807293 | Jul 2006 | US |
