MXPA98000263A - Titanium dioxide pigment similar to laminil - Google Patents

Abstract

The present invention relates to a lamella-like titanium dioxide pigment, free of substrate, which is obtained by the solidification of an aqueous solution of a thermally hydrolysable titanium compound on a continuous web, the detachment of the resulting layer, the coating of the resulting titanium dioxide lamellae, with or without intermediate drying, with more titanium dioxide by a wet method, and separation, drying and calcination of the obtained material

Description

TITANIUM DIOXIDE PIGMENT SIMILAR TO LAMINILLAS DESCRIPTION OF THE INVENTION The present invention relates to a pearlescent pigment of very thin titanium dioxide, based on lamellar-like titanium dioxide. For many years pearlescent pigments containing titanium dioxide have been successfully used. These are produced in accordance with the principle of substrate layers, mica being used virtually without exception as a substrate. Two main processes are known for the precipitation of the TiO2 layer. • First, the precipitation can be carried out in the manner described, for example, in US Patent No. 3,087,828, by adding a solution of titanyl sulfate, acidified with sulfuric acid, to the suspension of mica and carrying out the hydrolysis by heating to a temperature of about 100 ° C, wherein the layer thickness and the associated interference color are predetermined by the amount of titanyl sulfate present. Second, the precipitation can be carried out in the manner described, for example, in German Patent 2,009,566. In this case, the suspension REF: 26379 of mica is heated to a temperature of approximately 50 to 100 ° C, preferably to 70-80 ° C, an aqueous solution of titanium salt is added slowly and the pH is kept substantially constant at a value of about 0.5 to 5, in particular about 1.5 to 2.5, by the simultaneous addition of a base of a base, such as an aqueous solution of ammonia or an aqueous solution of an alkali metal hydroxide. As soon as the desired layer thickness of the Ti02 precipitate is reached, the addition of the titanium salt solution is stopped. A disadvantage of mica is that during the formation of titanium dioxide the formation of the anatase variant (octahedrite) is induced, although what is often desired is the rutile variant, which has a higher refractive index and more advantageous properties. Therefore, it is necessary to obtain the rutile variant by the addition of extraneous ions, especially tin ions (IV). Processes of this type are described, for example, in German Patents 2,213,545 and 2,522,572, wherein the rutilization is carried out by incorporating tin dioxide in the vicinity of the mica or in discrete layers between Ti02. However, other processes are also known, for example the incorporation of zinc oxide in accordance with Compound Patent 208,578; or the incorporation of iron (III) in the layer of TÍO2, in accordance with German Patent DE-C 1,959,998, where these processes produce rutile layers. Mica pigments are widely used in the printing and coating industry, in cosmetics and in polymer processing. These are distinguished by interference colors and a high luster. However, for the formation of extremely thin layers, the mica pigments are not suitable, since the same mica as substrate for the metallic oxide layers of the pigment, has a thickness of 200 to 1200 nm. A further disadvantage is that the thickness of the mica lamellae within a certain fraction defined by the size of the lamella sometimes varies significantly around an average value. In addition, mica is a mineral of natural origin that is contaminated by foreign ions. In addition, processing steps are technically very complex and time-consuming, including, above all, crushing and sorting. The pearlescent pigments based on thick mica lamellae and coated with metal oxides, due to the thickness of the edges, have a marked dispersion fraction, especially in the case of distributions of relatively fine particle sizes below 20 μm. As a substitute for mica it has been proposed to use thin glass flakes, which are obtained by grinding molten glass with a subsequent crushing. In fact, interference pigments based on such materials exhibit color effects superior to those of conventional mica-based pigments. However, the disadvantages are that the glass flakes have a very large average thickness of approximately 10 to 15 μm and a very wide thickness distribution (typically between 4 and 20 μm), while the thickness of the interference pigments is typically not greater than 3 μm. European Patent EP 0,384,596 describes a process in which a hydrated alkali metal silicate is subjected to temperatures of 480 to 500 ° C, with the action of an air jet, forming bubbles with thin walls; Subsequently, the bubbles are ground to obtain lamellar-like alkali metal silicate substrates having a thickness of less than 3 μm. However, the process is complex and the thickness distribution of the resulting lamellae is relatively broad.

German Patent DE 1,136,042 discloses a continuous web process for the preparation of oxides or hydrates of oxides similar to spangles or similar to metal lamellae of groups IV and V and of the iron group of the Periodic Table of the Elements. In this process, a release layer comprising, for example, a silicone coating, if desired, is first applied to a continuous band to facilitate the subsequent detachment of the metal oxide layer. Then, a liquid film of a solution of a hydrolyzable compound of the metal to be transformed into the desired oxide is applied and the film is dried and subsequently peeled off with a vibrating device. The thickness of the layer and the resulting lamellae is established as 0.2 to 2 μm, without giving specific examples of this. European Patents EP 0,240,952 and EP 0,236,952 have proposed a web process for the preparation of various lamellar-like materials, including silicon dioxide, aluminum oxide and titanium dioxide. In this process, a liquid film of defined thickness of a precursor of the lamella-like material is applied to a smooth web by a roller system; the film dries and falls off the band, forming lamella-like particles. Subsequently, the particles, if desired, are calcined, crushed and classified. The thickness of the lamellae obtained by the process described in European Patent EP 0,240,952 is relatively well defined, since the film, for example, is applied very uniformly to the web through a roller system. The thickness of the lamella layer given in the Examples is 0. 3 to 3.0 μm. In accordance with Example 1, a first roller is wetted with the precursor used, by a partial immersion of this roller in a container containing the precursor. The film is transferred from this roller onto a second rotating roller in the same direction, which is in very close contact with the first one. Finally, the film is applied by the second roller on the web. However, the disadvantages are the use of very expensive precursor materials and, in particular, the higher requirements in terms of safety in the workplace that must be applied when using organometallic compounds. To complete the chemical transformation of the precursor in the desired layer material, a strong heating of the film and the web material is generally required. In addition, the considerable thermal stress that occurs in the material of the band, the high energy consumption and the restriction in the speed of the process, are very disadvantageous for the profitability of the method. WO 93/08237 discloses lamellar-like pigments consisting of a lamella-like matrix comprising silicon dioxide, which may contain soluble or insoluble dyes and which is colored with one or more reflecting layers of metal oxides or metals. The lamella-like matrix is prepared by the solidification of water crystal (sodium silicate) on a continuous band. German Patent DE 1,273,098 describes the preparation of a pearl mother pigment by vapor deposition of films of ZnS, MgF2, ZnO, CaF2 and Ti02 on a continuous web. However, this process, similar to the process described in US Pat. No. 4,879,140 in which lamella-like pigments with Si and SiO2 layers are obtained by plasma phase deposition of SÍH4 and SÍCI4, is associated with very high costs in appliances. Despite numerous attempts, to date it has not been possible to develop any economic process to prepare very thin lamella-like titanium dioxide pigments having a layer thickness of less than 500 nm. The object of the present invention is to provide a pigment with highly lustrous pearly luster of titanium dioxide, having a layer thickness of less than 500 nm and a layer thickness tolerance of less than 10%, where the pigment contains virtually no foreign ions and is in the form of rutile or anatase. This object is achieved, in accordance with the present invention, by means of a lamellar-like substrate-free titanium dioxide pigment, which is obtained by the solidification of an aqueous solution of a thermally hydrolysable titanium compound on a continuous web, the detachment of the formed layer, the coating of the resulting titanium dioxide lamellae, with or without intermediate drying, with more titanium oxide by a wet process, and the separation, drying and calcination of the obtained material. The thermally hydrolysable titanium compound used is preferably in the form of an aqueous solution of titanium tetrachloride. The concentration of the titanium salt in this solution is from 7 to 30% by weight, preferably from 8 to 15% by weight. This objective is additionally achieved, according to the present invention, by a process for the preparation of the new pigment, in which a precursor of titanium dioxide similar to lamellae is applied in the form of a thin film to a continuous band, the liquid film solidifies by drying, during which the titanium dioxide is formed from the precursor by a chemical reaction, subsequently, the formed layer is stripped from the band and washed, the resulting titanium dioxide lamellae, with or without intermediate drying , they are suspended in water and coated with more titanium dioxide, and the coated titanium dioxide particles are separated from the aqueous suspension, dried and, if desired, calcined. After drying, the titanium dioxide is in the anatase form. When calcining above 600 °, it can be transformed without the presence of foreign ions, in the rutile form. By this means a highly pure titanium dioxide pigment is obtained in the rutile form, which is superior in many respects to conventional titanium dioxide pigments based on mica. If tin is incorporated into the Ti02 matrix, then the transformation to the rutile form is in fact carried out in the course of drying at 110 ° C. The present invention additionally relates to the use of the new pigment in paints with pigment, inks for printing, plastics, cosmetics and glass and ceramic glazing. For this purpose, it can also be used mixed with commercially available pigments, for example absorption pigments, metallic effect pigments and organic and inorganic LCP type pigments. The new pigment consists of titanium dioxide, similar to lamellae. These lamellae have a thickness between 10 and 500 nm, preferably between 40 and 300 nm. The value of the other two dimensions is between 2 and 200 μm and, in particular, between 5 and 50 μm. The new pigment is prepared in a two-stage process. In the first stage, the lamellae of titanium dioxide are produced with the aid of a continuous band. First, the web method will be explained with reference to Figure 1. The web 1, which is guided over a roller system 2, passes through an application unit 3, where it is coated with a thin film of the web. precursor. Suitable application units such as roller applicators and also flow units can be used. The speed of the band is from 2 to 400 m / minute, preferably from 5 to 200 m / minute. In order to achieve a uniform soaking of the plastic strip, it is necessary to add a commercially available wetting agent to the coating solution or activate the surface of the strip by flaming, corona treatment or ionization. The coated web subsequently runs through a drying zone 4, where the layer is dried at a temperature between 30 and 200 ° C. They can be used as dryers, for example, infrared dryers, air jet circulation dryers and commercially available ultraviolet dryers. After passing through the drying zone, the web is guided through the release containers 5, which contain an appropriate amount of release medium, for example completely deionized water, where the dried layer is removed from the web. . This detachment procedure is aided by additional devices, for example jets, brushes or ultrasound. The band is dried in a subsequent dryer 6 before re-coating. The continuous band must be made of a chemically and thermally resistant plastic, in order to ensure an adequate useful life and high drying temperatures. For this, materials such as polyethylene terephthalate (PET) or other polyesters and polyacrylates are suitable. The width of the film is typically between several centimeters and two or more meters. The thickness is from 10 μm to several mm, these two parameters being optimized with respect to the particular requirements. Additional details of the web processes can be obtained in US Patents 3,138,475; EP 0,240,952 and WO 93/0835. In a second stage of the process, the lamellae of titanium dioxide detached from the band are coated, without being dried in advance, with more titanium dioxide according to known methods. It is preferred to use the method described in US Pat. No. 3,553,001. An aqueous solution of titanium salt is slowly added to a slurry of the titanium dioxide slides, heated to a temperature of about 50 to 100 ° C, preferably 70 to 80 ° C, keeping the pH substantially constant at a value from about 0.5 to 5, preferably from about 1.5 to 2.5, simultaneously adding a base, for example an aqueous solution of ammonia or an aqueous solution of an alkali metal hydroxide. As soon as the desired thickness of the Ti02 precipitate layer is reached, the addition of the titanium salt solution is suspended. This process, which is also called the titration process, is notable for the fact that an excess of titanium salt is avoided. This is achieved by providing the hydrolysis, per unit of time, only that amount (of titanium salt) that is necessary for a uniform coating with the hydrated TIO2 and that can be absorbed, per unit of time, by the available surface of the particles to be coated. Therefore, there is virtually no formation of hydrated titanium dioxide particles that do not deposit on the surface to be coated. The amount of titanium salt added per minute, in this case, is of the order of about 0.01 to 2 x 10"mole of titanium salt per square meter of surface to be coated.In addition, the titanium dioxide lamellae can also be coating with more titanium dioxide, after drying, in a fluidized bed reactor by means of a gas phase coating, in which case, for example, the techniques proposed in European Patent EP 0,045,851 and EP 0,106,235 can be appropriately used. To prepare pearlescent pigments, the new pigment, in addition, can be coated with organic or inorganic dyes of firm adherence, low solubility, it is preferred to use colored lacquers and, in particular, aluminum colored lacquers. it applies a layer of aluminum hydroxide by precipitation and, in a second step, it is lacquered with a colored lacquer.The process is described in greater detail in the German Patents DE 2,429,762 and DE 2,928,287. Also preferred as additional coatings are pigments of complex salts, especially cyanoferrate complexes, for example Prussian blue and Turnbull, as described in European Patent EP 0,141,173 and DE 2,313,332. The new pigment can also be coated with organic dyes and, in particular, with phthalocyanine or metal phthalocyanine and / or indanthrene dyes, in accordance with German Patent DE 4,009,567. For this purpose, a suspension of the pigment is prepared in a solution of the dye and this suspension is subsequently mixed with a solvent in which the dye has little or no solubility. In addition, it is also possible to use metal chalcogenides or hydrated metal chalcogenides and carbon black. Additionally, it is possible to subject the pigment to a subsequent coating or a subsequent treatment, which increases the stability to light, the resistance to weathering and chemical stability or that facilitates the handling of pigment, especially its incorporation to different media. Examples of suitable subsequent coating and / or after-treatment techniques are those described in DE-C 2,215,191; DE-A 3,151,354; DE-A 3,235,017 or DE-A 3,334,598. The additionally applied substances constitute only about 0.5 to 5% by weight, preferably about 1 to 3% by weight of the total pigment. The pigment can be used in the conventional manner to pigment food, paints, printing inks, plastics, cosmetics and glazes for ceramics and glass. However, it can also be used for UV protection in cosmetic formulations or for industrial applications, since it excludes virtually all ultraviolet radiation in the range below 330 nm. As a result, the pigment is markedly superior to commercially available photoprotective filters. The concentration of the pigment in these formulations is from 0.1 to 30% by weight, preferably from 1 to 10% by weight. The protective action of the new pigment with respect to UV radiation was compared with that of Luxelen Silk D (manufacturer: Presperse, Inc.), which is a commercially available sunblock. For this purpose, the pigment (layer thickness: 130 nm) and the comparison product were incorporated into a NC lake (pigment concentration 1.7%), which was coated on a glass plate. After drying, the films were detached from the substrate and measured using a PE Lambda 19 instrument with an interconstructed integration sphere (Specacarol diaphragms increased, 30 nm) for transmission, reflection and absorption in the range of 200 to 2500 nm. The transmission of the film containing the new pigment is 0% below 330 nm, about 5% at 350 nm, 35% at 380 nm and 40% at 400 nm. The permeability for UV radiation below 350 nm, therefore, is much lower than that of the comparison product. In terms of thickness, the new pigment represents the ideal state which is the best that can be achieved with pigments with pearlescent luster. In the present case, the thickness of the lamellae corresponds to the layer thickness required for the optically functional layer of TiO2, whereas in the case of conventional pearlescent layered pigments, the lamella thickness can be greater by a factor of 25, since the thickness of the substrate, for example mica, is added to the functional layer. In terms of technical applications, this results in intrinsic advantages that can not be obtained with any other pigment with conventional pearl luster. For example, the paint coatings can be made thinner and the amount of pigment needed can be reduced, since, due to the absence of "filler" support materials, the pigments are optically more efficient. The following Examples are intended to illustrate the present invention, without limiting it. EXAMPLE 1 A circulating band of polyethylene terephthalate (width: 0.3 m, speed: 20 m / min) was coated with a solution of titanium tetrachloride % by means of a counter-rotating applicator roller. The coating solution contained 0.3% by weight of a surfactant (DISPERSE-AYD W-28, manufacturer: DANIEL PRODUCTS COMPANY). The aqueous film in the web was dried in a drying section by subjecting it to hot air at 70 ° C and the formed layer was detached from the web in a stripping pan filled with deionized water. The titanium dioxide particles were filtered and washed with completely deionized water. The lamellae showed a silver luster and a layer thickness of 100 ± 10 nm. To coat with more titanium dioxide, they were redisperged in completely deionized water. 2 1 of the Ti02 lamellar dispersion (solids content: 15 g TIO 2) of Example 1 was heated at 75 ° C and the pH was adjusted to a value of 2.2 with hydrochloric acid. Then an aqueous solution of 40% titanium tetrachloride was added at a rate of 3 ml / min and the pH was kept constant at 2.2 using 32% NaOH. The addition of TÍCI4 continued until the first order or higher order interference color was reached. The obtained pigment was filtered, washed with deionized water until it was free of salts, dried and calcined at 750 ° C. The color properties were not greatly altered as a function of the calcination temperature, in which context the anatase-rutile transformation, which starts at a temperature of about 600 ° C and ends at 750 ° C, plays an important role. EXAMPLE 2 Sunscreen cream Components Component A: Liquid paraffin 20.0% Cetyl alcohol 1.5% Beeswax 6.0% Stearic acid 20.0% PEO (5.5) cetyl ether 1.5% Sorbitol monostearate 2.5% Component B: 10% NaOH 1.0% Distilled water 36.5% Component C: Glycerol 6.0% Pigment of TÍO2 5.0% Preparation: The pigment was dispersed in glycerol. Components A and B were separately heated to 75 ° C and mixed in gel form with the aid of a high speed stirrer. Finally, component C was emulsified in the emulsion of A and B, at a temperature of 50 ° C. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as an antecedent, what is contained in the following is claimed as property.

Claims (2)

1. CLAIMS 1. A substrate-free lamella-like titanium dioxide pigment, characterized in that it is obtained by the solidification of an aqueous solution of a thermally hydrolysable titanium compound on a continuous web, the release of the resulting layer, the coating of the resulting titanium dioxide lamellae, with or without intermediate drying, with more titanium dioxide by a wet method, and the separation, drying and calcination of the obtained material. 2. A titanium dioxide pigment according to claim 1, characterized in that the thermally hydrolysable titanium compound used is an aqueous solution of titanium tetrachloride. 3. A process for the preparation of the titanium dioxide pigment according to any of claims 1 or 2, characterized in that - an aqueous solution of a thermally hydrolysable titanium compound is applied as a thin film to a continuous web, the liquid film solidifies by drying, during which the titanium dioxide is formed in the solution by a chemical reaction, subsequently, the formed layer is detached from the band and washed, the resulting titanium dioxide lamellae, with or without intermediate drying, they are suspended in water and coated with more titanium dioxide, and the titanium dioxide lamellae are separated from the aqueous suspension, dried and, if desired, calcined. 4. A titanium dioxide pigment according to claim 3, characterized in that the aqueous solution of a thermally hydrolysable titanium compound used is a solution of titanium tetrachloride. 5. A process according to any of claims 3 or 4, characterized in that the additional titanium dioxide is applied to the titanium dioxide lamellae dried in a fluidized bed reactor, by means of CVD. 6. The use of the pigments according to any of claims 1 or 2 for pigmenting paints, inks for printing, plastics, cosmetics and glazes for ceramics and glass, as well as in food and sunscreen. The use according to claim 6, characterized in that the pigments are used in the form of mixtures with commercially available pigments. 8. Paints, inks for printing, plastics, cosmetics, ceramics and glassware pigmented with a pigment according to any of claims 1 or
2. 2.