KR20000029474A - Metal oxide coated titanium dioxide lamellas - Google Patents

Abstract

PURPOSE: Colored nacreous pigments comprising a platelet-form TiO2 core with one or more layers of other metal oxides (or their hydrates) are provided. CONSTITUTION: Colored nacreous pigments are produced by deposition from an aqueous solution of a thermally hydrolyzable Ti compound on an endless belt, detachment of the resulting platelets and wet process coating of the platelets (with or without intermediate drying) with the metal oxide(s), followed by separation-off, drying and optional calcining of the product. The production process is also provided. The thermally hydrolyzable starting material is an aqueous TiCl4 solution and the other metal oxide is Fe2O3, Fe3O4, FeOOH or Cr2O3. Drying of the product pigment is at 110-150°C and calcining is at 400-700°C. Application of the other metal oxide is in a fluidised bed by CVD.

Description

Titanium dioxide plate-shaped metal oxide coating {METAL OXIDE COATED TITANIUM DIOXIDE LAMELLAS}

Mika-based pearlescent pigments with a metal oxide layer further on the titanium dioxide layer are known. U.S. Patent Nos. 3 087 828 and 3 087 829 disclose aluminum oxide, zirconium oxide, zinc oxide and tin oxide as colorless oxides for the second metal oxide layer, and iron oxide, nickel oxide, cobalt oxide, Mention is made of copper oxide and chromium oxide. Deposition of a second metal oxide on the titanium dioxide hydrate layer results in a clear stabilization of the photosensitivity of this layer. In particular, iron oxide-containing titanium dioxide pigments have been used successfully for a long time.

U.S. Patent No. 30 87 828 discloses that a gold-colored mica pigment with a red tint upon calcination is obtained by depositing a Fe ₂ O ₃ layer on a TiO ₂ layer.

U.S. Patent No. 3 874 890 discloses a process for the preparation of gold-coloured pearlescent pigments in which a mica pigment coated with TiO ₂ and / or ZrO ₂ is first coated with iron (II) hydroxide and then oxidized with Fe ₂ O ₃ . This is described.

U.S. Patent No. 4 744 832 discloses that the metal oxide layer contains both titanium and iron, and the pigment has a multi-layered structure (upper brookite layer and iron oxide layer after the first layer of TiO ₂ in rutile form). , Pearlescent pigments based on a plate-like substrate coated with a metal oxide, in particular mica.

Mica pigments are widely used in the printing and coatings industry, cosmetics and polymer processing. They are characterized by interference colors and high gloss. However, in order to form a very thin layer, the mica pigment is not suitable because the mica itself has a thickness of 200 to 1200 nm as a substrate for the metal oxide layer of the pigment. A further disadvantage is that in some cases the thickness of the mica plate within any fraction defined by the plate size clearly varies around the mean. Moreover, mica is a natural inorganic substance contaminated by external ions. Moreover, there is a need for technically very complex and time-consuming processing steps, in particular grinding and sorting.

Pearlescent pigments based on thick mica plates and coated with metal oxides have a significant scattering fraction, especially in the case of comparatively fine particle size distributions of 20 μm or less due to the thickness of the edges.

As substituents for mica, it has been proposed to use thin glass flakes obtained by rolling and then grinding glass melts. In addition, interference pigments based on these materials exhibit superior color effects than conventional mica-based pigments. However, a disadvantage is that although the thickness of the interference pigment is typically on the order of 3 μm, the glass flakes have a very large average thickness of about 10 to 15 μm and a very wide average thickness distribution (typically 4 to 20 μm).

European Patent No. 0,384,596 sends hydrated alkali metal silicate to a temperature of 480 to 500 ° C. under the action of an air jet and forms bubbles with thin walls; Subsequently, the method of subdividing the foam to obtain a plate-like alkali metal silicate substrate having a thickness of less than 3 μm is described. However, this method is complicated and the resulting plate thickness distribution is relatively wide.

German Patent No. 11 36 042 describes a continuous belt process for producing plate-like or shiny oxides or oxide hydrates of metals of groups IV and V and iron groups of the Periodic Table of Elements. In this method, for example, an emissive layer comprising a silicone coating is optionally first applied to the continuous belt to facilitate subsequent desorption of the metal oxide layer. A liquid film comprising a solution of the hydrolyzable compound of the metal which is converted into the desired oxide is then applied, and the film is dried and subsequently desorbed using a vibrating device. Although no specific example thereof is given, the plate-like layer thickness obtained is given as 0.2 to 2 m.

European Patent Nos. 0,240,952 and 0,236,952 propose a continuous belt method for producing other plate-like materials comprising silicon dioxide, aluminum oxide and titanium dioxide. In this method, a thin liquid film of defined thickness of the precursor of the plate material is applied to the smooth belt through the roller system; The film is dried, detached from the belt, and platelets are formed. Subsequently, the particles are optionally calcined, ground and classified.

The plate-like thickness obtained according to the method described in EP 0 240 952 is relatively well defined, for example, because the film is very uniformly applied to the continuous belt via the roller system. The plate-like layer thickness is given as 0.3 to 3.0 μm in the examples. According to Example 1, the first roller is wetted with the precursor used by partially incorporating the first roller into the raw material container filled with the precursor. The film is transferred from the first roller to a second idle roller in very close contact with the first roller. Finally, the film is rolled out from the second roller onto the continuous belt.

However, a disadvantage is the use of very expensive precursor materials, in particular the strengthening of workplace safety conditions that must be applied when organometallic compounds are used. Complete chemical conversion of the precursor to the desired layer material generally requires strong heating of the film and belt material. In addition to the significant thermal stresses placed on the belt material, this method is very disadvantageous in terms of economics of the method due to the large energy consumption and the limitation of the process speed.

WO 93/08237 describes a plate pigment composed of a plate-like matrix comprising silicon dioxide, which may contain soluble or insoluble colorants and is covered with one or more reflective layers of metal oxides or metals. The plate matrix is produced by solidification of water glass on a continuous belt.

German Patent 1 273 098 describes the preparation of mother-of-pearl pigments by depositing ZnS, MgF ₂ , ZnO, CaF ₂ and TiO ₂ films onto a continuous belt. However, this method entails a very high cost of the device, such as the method described in US Pat. No. 4,879,140, in which platelet pigments having Si and SiO ₂ layers are obtained by plasma deposition from SiH ₄ and SiCl ₄ .

Despite numerous attempts, no economic method has been developed so far to produce very thin plate-like titanium dioxide pigments having a layer thickness of less than 500 nm.

The present invention relates to very thin pearlescent pigments based on metal oxide coated or metal oxide hydrate coated plated titanium dioxide.

It is an object of the present invention to provide a very shiny pearlescent titanium dioxide-containing pigment having a layer thickness of less than 500 nm and a layer thickness tolerance of less than 10%.

This purpose is to solidify an aqueous solution of thermally hydrolyzable titanium compound on a continuous belt, desorption of the resulting layer, cover the titanium dioxide plate produced by the wet process with or without the drying step, and separate and separate According to the invention by means of pearlescent pigments having a multilayer structure with a layer of other metal oxides or metal oxide hydrates on the core of plate-shaped titanium dioxide, which can be obtained by drying and optionally by calcination of the obtained material. .

Other metal oxides or metal oxide hydrates applied to titanium dioxide are Fe ₂ O ₃ , Fe ₃ O ₄ , FeOOH, Cr ₂ O ₃ , CuO, Ce ₂ O ₃ , Al ₂ O ₃ , SiO ₂ , BiVO ₄ , NiTiO ₃ , CoTiO ₃ and also antimony-doped, fluorine-doped or indium-doped titanium oxide.

In a particular embodiment of the novel pigments, there is also a third layer of additional metal oxide or metal oxide hydrate on the second layer of other metal oxide or metal oxide hydrate. This additional metal oxide or metal oxide hydrate can be selected from aluminum oxide or aluminum oxide hydrate, silicon dioxide or silicon dioxide hydrate, Fe ₂ O ₃ , Fe ₃ O ₄ , FeOOH, ZrO ₂ , Cr ₂ O ₃ as well as antimony-doped, Fluorine-doped or indium-doped titanium oxide.

The aqueous solution of the thermally hydrolyzable titanium compound for the production of titanium dioxide platelets on a continuous belt is preferably an aqueous solution of titanium tetrachloride.

The concentration of titanium salt in these solutions is 7 to 30% by weight, preferably 8 to 15% by weight.

This object is further achieved according to the invention by a process for the preparation of a novel pigment comprising the following steps:

Applying an aqueous solution of the thermally hydrolyzable titanium compound to the continuous belt as a thin film,

Developing titanium dioxide from the solution by chemical reaction, while drying to solidify the liquid film,

Subsequently removing and washing the resulting layer from the belt,

In the presence or absence of a drying step, the obtained titanium dioxide platelets are suspended in water and coated with other metal oxides and optionally further metal oxides, and

Separating the coated titanium dioxide platy from the aqueous suspension, drying and optionally calcining.

In addition, after drying in between, a titanium dioxide plate-like coating can be carried out with a metal oxide or metal oxide hydrate layer in a fluidized bed reactor, for example by vapor phase coating, for example in EP 0,045,851 and 0,106,235. The proposed method of making pearlescent pigments can be used.

Moreover, the invention relates to the use of the pigments according to the invention for coloring paints, printing inks, plastics, cosmetics, and varnishes for ceramics and glass.

For this purpose, mixtures with commercially available pigments such as inorganic and organic adsorption pigments, metal effect pigments and LCP pigments can be used.

The novel pigments are based on platy titanium dioxide. These platelets have a thickness of 10 to 500 nm, preferably 40 to 150 nm. The two different dimensions range from 2 to 200 μm, in particular from 5 to 50 μm.

The other layer of metal oxide applied on the titanium dioxide plate has a thickness of 5 to 300 nm, preferably 5 to 150 nm.

The novel pigments are made in a three step process. In the first step, the plate-shaped titanium dioxide particles are made into a continuous belt.

First, the belt method will be described with reference to FIG.

The continuous belt 1 sent through the roller system 2 passes through the applicator unit 3 and is covered with a thin film of precursor in the applicator unit 3. Suitable applicator units that can be used are roller applicators and also flowable units. The belt speed is 2 to 400 m / min, preferably 5 to 200 m / min.

In order to achieve uniform wetting of the plastic belt, it is appropriate to add commercially available wetting agents to the coating solution or to activate the surface of the belt by flame treatment, corona treatment or ionization.

The coated belt subsequently passes through the drying section 4 and in the drying section 4 the layer is dried at a temperature of 30 to 200 ° C. As the dryer, commercially available infrared circulation-air jets and UV dryers can be used, for example.

After passing through the drying section, the belt passes through a desorption bath 5 containing a suitable desorption medium, for example demineralized water, to remove the layer dried in the desorption bath 5 from the belt. The desorption process is supported by additional devices, for example jets, brushes or ultrasonics.

In the subsequent dryer 6, the belt is dried before recoating.

Continuous belts must be made from chemical and heat resistant plastics to ensure proper service life and high drying temperatures. Suitable materials for the belt include polyethylene terephthalate (PET) or other polyesters and polyacrylates.

The film width is typically a few cm to at least 2 m. The thickness is from 10 μm to several mm and these two parameters are optimized for special needs.

Further details of the continuous belt method are known from US Pat. No. 3,138,475, EP 0 240 952 and WO 93/08237.

In the second process step, the plate of titanium dioxide detached from the belt is coated with another metal oxide according to a known method without drying beforehand.

When coated with large magnets (Fe ₂ O ₃ ), the starting materials are for example the iron (III) salts described in US Pat. Nos. 3,987,828 and 3 087 829, or US Pat. No. 3,874,890. It may be an iron (II) salt, and the initially formed coating of iron (II) hydroxide is oxidized with iron (III) oxide hydrate. Iron (III) salts are preferably used as starting materials. For this purpose, the iron (III) chloride solution is metered into an aqueous suspension on a titanium dioxide plate at a temperature of 60 to 90 ° C. and a pH of 2.5 to 4.5. The pH is kept constant by the simultaneous addition of 32% sodium hydroxide solution. After workup and drying at 110 ° C., a red pigment is obtained.

Coating with magnetite (Fe ₃ O ₄ ) is carried out by hydrolysis of an iron (II) salt, for example iron (II) sulfate solution, at a pH of 8.0 in the presence of potassium nitrate. Examples of particular depositions are described in EP 0,659,843. Black pigments are obtained after workup and drying at 100 ° C.

It is also preferred to coat the titanium dioxide platelets with yellow FeO (OH) in goethite modification. In this case, the FeSO ₄ aqueous solution is metered into a suspension of titanium dioxide plate at 70 ° C. under a nitrogen atmosphere. The pH is then adjusted to 4 with 10% Na ₂ CO ₃ solution and oxygen is sent to the suspension. After workup and drying at 110 ° C., a yellow pigment is obtained. For exact deposition conditions, see European Patent No. 0,659,843.

In order to adhere the iron oxide layer well onto the titanium dioxide plate, it is appropriate to first apply a tin oxide layer. In this method, the SnCl ₄ solution treated with hydrochloric acid is added to the titanium dioxide plate-shaped suspension, adjusted to a pH of 1.8, and the pH is kept constant by simultaneous addition of 32% sodium hydroxide solution. After deposition of the tin dioxide hydrate layer, it can then be immediately coated with iron oxide hydrate.

Another metal oxide that is preferably deposited on a titanium dioxide plate is chromium oxide.

Deposition can be easily carried out by thermal hydrolysis in which volatilization of ammonia takes place from an aqueous solution of hexamine-chromium (III) derivative, or by thermal hydrolysis of a chromium salt solution buffered with borax. Coatings with chromium oxide are described in US Pat. Nos. 3 087 828 and 3 087 829.

The novel pigments need not be calcined in all cases. For any application, drying at a temperature of 110 ° C. is sufficient. When the pigment is calcined, a temperature of 400 ° C to 1000 ° C is set, preferably 400 ° C to 700 ° C.

In addition, the novel pigments can be coated by firmly bonding low solubility inorganic and organic colorants. Preference is given to using color rakes, in particular aluminum color rakes. For this purpose, an aluminum hydroxide coating is applied by deposition and rake with a color rake in a second step. This method is described in more detail in German Patent Nos. 24 29 762 and 29 28 287.

Further coatings with complex salt pigments, in particular cyanoferrate complexes, for example Prussian blue and Turnbull's blue, described in European Patent Nos. 0 141 173 and 23 13 332 Also preferred.

The novel pigments can also be coated with organic dyes, in particular phthalocyanine or metal phthalocyanine and / or indanthrene dyes according to German Patent No. 40 09 567. For this purpose, a pigment suspension in a dye solution is prepared, which is then sent with the solvent so that the dye is of low or zero solubility.

Moreover, metal chalcogenide or metal chalcogenide hydrate and carbon black can also be used for further coating.

The pigment may be further treated with a post-coating or post-treatment which further increases light stability, weather resistance or chemical stability, or facilitates handling of the pigment, in particular incorporation into other media. Examples of suitable aftercoat techniques are for example the methods described in German Patent Nos. C 22 15 191, A 31 51 354, A 32 35 017 or A 33 34 598. Because of the fact that the properties of the novel pigments are already very good without these further measurements, these optional additionally applied materials constitute only about 0 to 5% by weight, especially about 0 to 3% by weight of the total pigment.

In terms of thickness, the new pigment is the best that can be made of pearlescent pigments, since it consists only of an optically functional functional layer and is free of other conventional support materials, such as mica or glass flakes, which do not contribute to optical effects. The abnormal state is shown. Because of the thickness of the mica, the mica pigment has a thickness larger by a factor of 25 or less for a functional layer of a given thickness. In terms of technical application, this provides an inherent advantage over other conventional pearlescent pigments. For example, because the pigment is more optically active due to the absence of the support material "filler", the paint layer can be made thinner and the amount of pigment required can be reduced.

The examples given below are intended to illustrate the invention and do not limit it.

Example 1

The circulation belt of polyethylene terephthalate (width: 0.3 m, speed: 20 m / min) is coated with 20% titanium tetrachloride solution by an applicator roll rotating in reverse. The coating solution contains 0.3% by weight of surfactant (DISPERSE-AYD W-28, manufactured by DANIEL PRODUCTS COMPANY). The aqueous film on the belt is dried in the drying section by contacting hot air at 70 ° C., and the formed layer is detached from the belt at the desorption section filled with demineralized water. The plate-shaped titanium dioxide particles are filtered off and washed with demineralized water. The plate has a silver gloss and a layer thickness of 100 ± 10 nm. For the coating of other metal oxides, they are redispersed in demineralized water.

2 l of dispersion (solid content: 15 g of TiO ₂ ) are heated to 75 ° C. and adjusted to a pH of 1.8 with dilute hydrochloric acid.

4.3 g of SnCl ₄ .5H ₂ O are dissolved in 29 ml of HCl, the solution is made up to 290 ml with distilled water and stirred for 10 minutes.

SnCl ₄ solution is added to the TiO ₂ suspension at a rate of 3 ml / min, during which the pH is kept constant at 1.8 with 32% NaOH solution. After coating with SnO ₂ , the suspension is stirred for 15 minutes at constant temperature and constant pH.

The pH is then adjusted to 3.0 using 32% NaOH solution, 8% aqueous iron (III) chloride solution is metered at a rate of 3 ml / min, and the pH is kept constant by simultaneous addition of NaOH solution. . Continue adding FeCl ₃ until the desired interference color is achieved. The pigment obtained is filtered off, washed with demineralized water and dried at 110 ° C. for 12 h. Pigments have the desired interference color and red body color.

Claims (11)

The aqueous solution of the thermally hydrolyzable titanium compound is solidified on a continuous belt, the resulting layer is desorbed, and the titanium dioxide platelets produced by the wet method in the presence or absence of the drying step are covered with one or more other metal oxides or other metal oxide hydrates. Consisting of a core of plate-shaped titanium dioxide and one or more layers of other metal oxides or metal oxide hydrates, which can be obtained by separation, drying, drying and optionally calcination of the obtained material. Colored pearl luster pigments. The method of claim 1, Pearl luster pigment, characterized in that the other metal oxide is Fe ₂ O ₃ , Fe ₃ O ₄ , FeOOH or Cr ₂ O ₃ . (1) applying an aqueous solution of a thermally hydrolyzable titanium compound as a thin film to a continuous belt, (2) developing titanium dioxide from the solution by chemical reaction while drying to solidify the liquid film, (3) subsequently removing and washing the resulting layer from the belt, (4) suspending the obtained plate of titanium dioxide in water with or without the drying step and coating with at least one metal oxide, and (5) separating the coated titanium dioxide platy from the aqueous suspension, drying and optionally calcining A method for producing a pearlescent pigment according to claim 1. The method of claim 3, wherein An aqueous solution of a thermally hydrolyzable titanium compound is a titanium tetrachloride aqueous solution. The method according to claim 3 or 4, Wherein the other metal oxide used is Fe ₂ O ₃ , Fe ₃ O ₄ , FeOOH or Cr ₂ O ₃ . The method according to any one of claims 3 to 5, The pigment is dried at a temperature of 110 to 150 ℃. The method according to any one of claims 3 to 6, The pigment is calcined at a temperature of 400 to 700 ° C. The method according to any one of claims 3 to 7, Another metal oxide or additional metal oxide is applied on the titanium dioxide plate in a fluidized bed reactor by chemical vapor deposition (CVD). For coloring paints, printing inks, plastics, cosmetics, and varnishes for ceramics and glass Use of the pigment according to claim 1. The method of claim 9, The pigments are used as a mixture with commercially available pigments. Paints, printing inks, plastics and cosmetics colored with the pigments according to claim 1.