KR20000029486A - Multi-coated interference pigments - Google Patents

Abstract

PURPOSE: Multilayer interference pigments provide strong interference color and/or transparent interference pigments having strong dependability of angle for the interference color, which include only optical active layer. CONSTITUTION: Multilayer interference pigments are provided which consist of a TiO2platelet substrate with alternating layers of low and high RI (difference at least 0.1) metal oxides, production being by depositing and hydrolyzing an aqueous solution of a thermally hydrolyzable Ti compound on an endless belt, followed by detaching, wet process coating the resulting TiO2 platelets (with or without intermediate drying) with alternating coatings of low and high RI metal oxide hydrates by hydrolysis of the corresponding water-soluble metal compounds, separating off the product and drying and optionally also calcining it.

Description

Multi-coated interference pigments

Known multilayered pigments have low transparency. The metal oxide layer is prepared by (1) precipitation of a metal oxide hydrate from a metal salt solution onto a carrier material by a wet method, or (2) by vapor deposition or sputtering under reduced pressure.

In general, the deposition method is too complicated and expensive when mass producing pigments. Thus, U. S. Patent No. 4,434, 010 discloses a dielectric material having a transparent and high refractive index (e.g. titanium dioxide) and a dielectric material having a transparent and low refractive index on both a center layer of light reflecting material (aluminum) and a center aluminum layer. Multilayer interference pigments are described that consist of alternating layers of material (eg, silicon dioxide). This pigment is used for printing securities.

Japanese Patent Publication No. H7-759 describes a multilayer interference pigment having a metallic luster. This pigment comprises a support coated with alternating layers of titanium dioxide and silicon dioxide. The support is formed from flakes of aluminum, gold or silver or platelets of mica and glass coated with a metal. Thus, this pigment is a pigment that exhibits a typical metal-effect. However, this pigment is very opaque, which is inadequate when colored materials with high transparency are required, for example for films used in agriculture. In addition, since it completely reflects light in the metal layer forming the center, many pigment particles cannot interact with light, so that the depth effect of typical interference pigments does not appear. Therefore, the interference effect is only limited to the coating layer on the metal layer.

Mica is the support most often used in the production of interference pigments.

Mica pigments are widely used in the printing and coatings industry, cosmetics and polymer processing. Mica pigments are characterized by interference color and excellent gloss. However, when trying to form a very thin coating layer, the mica pigment is not suitable because the mica itself, which is the support of the metal oxide coating layer of the pigment, has a thickness of 200 to 1200 nm. In addition, in some cases the disadvantage is that the average value of the mica platelet thickness varies widely. In addition, mica is a natural mineral with a mixture of external ions. Moreover, there is a need for technically very complex and time-consuming manufacturing steps, in particular grinding and sorting.

Pearlescent pigments based on thick mica platelets and coated with metal oxides have large scattering rates by the thickness of the edges, especially when they have a relatively fine particle size distribution of less than 20 μm.

As a substitute for mica, the use of thin glass flakes obtained by rolling and pulverizing molten glass has been proposed. In fact, interference pigments based on thin glass flakes exhibit superior color effects than conventional mica based pigments. However, glass flakes have a very large average thickness of about 10 to 15 μm and a very wide thickness distribution (typically 4 to 20 μm), but have the disadvantage that the thickness of the interference pigment is typically no greater than 3 μm.

EP 0,384,596 discloses hydrated alkali metal silicates to form thin walled bubbles with an air injector at a temperature of 480 to 500 ° C .; A method is then described in which bubbles are crushed to provide platelet-shaped alkali metal silicate supports having a thickness of less than 3 μm. However, this method is complex and the thickness distribution of the resulting platelets is relatively wide.

German Patent No. 11 36 042 describes a continuous belt process for producing oxides or oxide hydrates of group 4 and 5 metals and iron groups of the periodic table, either platelet or shiny. In this method, if desired, for example, a silicone coated release layer is first applied to the continuous belt to facilitate separation of the metal oxide layer. A liquid film comprising a solution of the hydrolyzable compound of the metal to be converted to the desired oxide is then applied, the liquid film is dried and then separated using a vibrating device. The coating layer thickness of the obtained platelets is provided at 0.2 to 2 mu m, but specific examples thereof are not mentioned.

EP 0 240 952 and EP 0 236 952 describe a continuous belt process for producing different platelet-like materials, including silicon dioxide, aluminum oxide and titanium dioxide. In this method, a thin liquid film consisting of a precursor of platelet-shaped material having a defined thickness is applied to a soft belt via a roller system. The film is dried and separated from the belt to form platelet-shaped particles. The particles are then calcined, ground and classified as necessary.

The thickness of the platelets obtained according to the method described in EP 0 240 952 is relatively well defined because the film is applied very uniformly to the continuous belt, for example via a roller system. The layer thickness of the platelets is provided in the examples from 0.3 to 3.0 μm. According to Example 1, the first roller is partially immersed into the storage container filled with the precursor and wetted with the precursor used. The wet film is moved from the first roller to a second corotating roller very close to the first roller. Finally, the film is transferred from the second roller onto the continuous belt.

However, this method has the disadvantage of using very expensive precursor materials, and particularly high workplace safety requirements to be applied when using organometallic compounds. In general, high temperature heating of the film and belt materials is required to completely convert the precursor chemically to the desired coating material. In addition to the significant thermal stresses exerted on such belt materials, this method is also economically disadvantageous due to the high energy consumption and the limitation of the production rate.

International Patent Publication No. WO 93/08 237 describes platelet-shaped pigments composed of a platelet-like matrix comprising silicon dioxide, which may comprise water-soluble or insoluble colorants, which may comprise metal oxides or metals. Coated with one or more reflective layers. Platelet-shaped matrices are prepared by solidification and hydrolysis of water glass in a continuous belt.

German Patent No. 12 73 098 describes a process for preparing nacre pigments by depositing ZnS, MgF ₂ , ZnO, CaF ₂ and TiO ₂ films on a continuous belt. However, as with the method described in US Pat. No. 4,879,140, which obtains platelet-shaped pigments having Si and SiO ₂ coating layers from SiH ₄ and SiCl ₄ by plasma deposition method, this method is very expensive.

The present invention relates to a multilayer interference pigment having platelet-shaped titanium dioxide as a support.

It is an object of the present invention to provide an essentially transparent interference pigment having a strong interference color and / or strong angle dependence of the interference color. It is also an object of the present invention to provide very thin pigments comprising only an optically functional layer.

The object of the present invention is to: ① solidify and hydrolyze an aqueous hydrolyzable titanium compound solution on a continuous belt, ② separate the resulting coating layer of titanium dioxide, and ③ in the presence or absence of the drying step by a wet method, The platelets of titanium dioxide produced in ② are alternately coated with a metal oxide hydrate having a high refractive index and a metal oxide hydrate having a low refractive index, ④ hydrolyzing the corresponding water soluble metal compounds, ⑤ separating the material thus obtained, As a carrier material, platelet-shaped titanium dioxide, alternately coated with a metal oxide layer having a high refractive index and a metal oxide layer having a low refractive index, which can be obtained by drying and calcining as needed, having a refractive index difference of 0.1 or more Is achieved by a multilayer interference pigment.

This object is also achieved by the following process for producing the novel pigments according to the invention:

① Apply thermally hydrolyzable aqueous titanium compound solution to the continuous belt as a thin film;

(2) While the titanium dioxide is produced by a chemical reaction in an aqueous solution, the liquid film is dried and solidified;

③ The resulting layer is then washed off the belt;

④ With or without the drying step, the obtained titanium dioxide platelets are suspended in water, and hydrolyzed metal compounds of a metal oxide hydrate having a high refractive index and a metal oxide hydrate having a low refractive index are added and hydrolyzed to have a high refractive index. Alternately coating with metal oxide hydrate and metal oxide hydrate having a low refractive index;

(5) The coated titanium dioxide platelets are separated from the aqueous suspension, dried and calcined as necessary.

The invention also relates to coloring paints, printing inks, plastics, cosmetics; Glazes of porcelain and glass; And the use of novel pigments for the production of agricultural films.

The novel pigments for this purpose can be used as a mixture with commercially available pigments (eg inorganic and organic absorbing pigments), pigments exhibiting a metallic effect and LCP pigments.

The novel pigments are based on platelet-shaped titanium dioxide. These platelets have a thickness of 10 to 500 nm, preferably 40 to 150 nm. The other two dimensions have a size of 2 to 200 μm, in particular 5 to 50 μm.

Metal oxides with high refractive indices may be oxides or mixtures of oxides (eg TiO ₂ , ZrO ₂ , Fe ₂ O ₃ , Fe ₃ O ₄ , Cr ₂ O ₃ , or ZnO) or with absorptive or high refractive indices Compounds (eg, iron titanate, iron oxide hydrate and titanium suboxide) or mixtures between these compounds or mixtures with other metal oxides and / or mixed phases.

Metal oxides having a low refractive index are SiO ₂ , Al ₂ O ₃ , AlOOH, B ₂ O _3, or mixtures thereof and likewise have absorbency or non-absorption. If desired, the oxide layer having a low refractive index may contain, as constituents, alkali metal oxides and alkaline earth metal oxides.

The thickness of the metal oxide layer having a high refractive index and the metal oxide layer having a low refractive index is important in the optical properties of the pigment. Since a product with a dark interference color is preferred, the thicknesses of the layers must be adjusted relative to each other. When n is the refractive index of the layer and d is the thickness of the layer, the color that appears in the thin layer is the product of n and d, i.e. the optical thickness. When generated by normal incident light upon reflection of light, the color of such a film having an optical thickness is characterized by the enhancement of light having a wavelength of λ = (4 / 2N-1) nd and of λ = (2 / N) nd This is the result of the reduction of light with a wavelength. In the above formulas, N is a positive integer. The change in color that occurs as the thickness of the film increases is the result of the enhancement or reduction of light having a particular wavelength by interference. For example, a 115 nm thick film of titanium dioxide with a refractive index of 1.94 has an optical thickness of 115 × 1.94 = 223 nm, and light having a wavelength of 2 × 223 nm = 446 nm (blue) during the reflection process. The reduced and reflected light becomes yellow. In the case of multilayer pigments, the interference color is determined by enhancement of a particular wavelength, and if two or more layers in the multilayer pigment have the same optical thickness, the color of the reflected light becomes darker and darker as the number of layers increases. In addition, an appropriate choice of layer thickness can cause particularly noticeable color changes depending on the viewing angle. It may be desirable for the pigments according to the invention for a pronounced color reduction to occur. The thickness of each metal oxide layer is therefore 20 to 500 nm, preferably 50 to 300 nm, regardless of the refractive index.

The number and thickness of layers depends on the desired effect. In general, the desired effect is achieved when a five-layer system of TiO ₂ / SiO ₂ / TiO ₂ / SiO ₂ / TiO ₂ is constructed and the thickness of each layer is optically coordinated with each other. When using an optically relatively thin TiO ₂ layer (layer thickness <100 nm), for example, it is possible to produce an interference pigment with a deeper and clearer blue color with a significantly smaller amount of TiO ₂ than a pure TiO ₂ -mica pigment. have. TiO ₂ can be saved up to 80% by weight or less.

A thick SiO ₂ layer (layer thickness> 100 nm) is precipitated to give a pigment with very pronounced angle dependence of the interference color.

It is also possible to further precipitate the SiO ₂ and TiO ₂ layers to obtain an advanced system and to limit the number of layers to suit the economics of the pigments.

In contrast to mica, since platelet-shaped titanium dioxide used as a support is an optically functional layer, covering the support with, for example, two layers having the above structure, consists of a thin five-layer interference system with exactly defined thickness. To provide. The reflection or transmission spectra of the pigments represent structures that can be harmonized more finely and more accurately than the spectra of corresponding pigments based on supports having a wide thickness distribution, such as mica.

Even in very thin TiO ₂ layers (layer thickness: 40 nm), these pigments exhibit a dark interference color. The angle dependence of the interference color is also particularly pronounced. Very severe color reduction is not observed with conventional metal oxide-mica pigments.

The novel pigments are prepared in a two step process. In the first step, platelet-shaped titanium dioxide particles are produced in a continuous belt.

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

The continuous belt 1 guided via the roller system 2 passes through an applicator device 3 which coats with a thin film of a thermally hydrolyzable titanium compound aqueous solution. It is preferable to use an aqueous titanium tetrachloride solution. The concentration of titanium salt in this solution is 7 to 30% by weight, preferably 8 to 15% by weight. Suitable applicator devices that can be used are roller applicators and also flowable devices. The belt speed is 2 to 400 m / min, preferably 5 to 200 m / min.

In order to uniformly wet the plastic belt, it is convenient to add commercially available wetting agents to the coating solution or to activate the belt surface by flame treatment, corona treatment or ionization.

The coated belt then passes through a drying zone 4 where the coating layer is dried at a temperature of 30 to 200 ° C. As the dryer, commercially available infrared, circulating air injectors and ultraviolet dryers can be used, for example.

After passing through the drying zone, the belt is passed through a separation bath 5 comprising a suitable separation medium, for example deionized water, to remove the dried layer from the belt. The separation process takes place by means of an additional device, for example an injector, a brush or an ultrasonic wave.

In the dryer 6 then the belt is dried before it is coated again.

Continuous belts should be made of chemical and heat resistant plastics to maintain a good shelf life and high drying temperature. Suitable materials for the belt include polyethylene terephthalate (PET) or other polyesters and polyacrylates.

The film width is typically from several centimeters to two meters or more. The thickness is from 10 μm to several mm and these two variables are optimized according to the specific requirements.

A more detailed description of the continuous belt method is known from US Pat. No. 3,138,475, EP 0 240 952 and WO 93/08 237.

In the second step, the platelets of titanium dioxide separated from the belt are alternately coated with metal oxide hydrates with low refractive index and metal oxide hydrates with high refractive index, without predrying.

The metal oxide layer is preferably applied by a wet chemical method, which can be one of the wet chemical coating techniques developed for producing pearlescent pigments. Techniques of this kind are described, for example, in German Patent No. 14 67 468, German Patent No. 19 59 988, German Patent No. 20 09 566, German Patent No. 22 14 545, German Patent No. 22 15 191, Germany Patent No. 22 44 298, German Patent No. 23 13 331, German Patent No. 25 22 572, German Patent No. 31 37 808, German Patent No. 31 37 809, German Patent No. 31 51 343, German Patent No. 31 51 354, German Patent No. 31 51 355, German Patent No. 32 11 602, German Patent No. 32 35 017, or else further patent literature and other publications.

In the case of a wet coating, the support particles are suspended in water and then at least one hydrolyzable metal salt at a selected pH suitable for hydrolysis and so that the metal oxide and / or metal oxide hydrate can precipitate directly on the platelets without secondary precipitation. Add. The pH is usually kept constant by simultaneous metered addition of bases. The pigments are then separated, washed, dried and calcined as needed, with the calcination temperature optimized according to the particular coating layer present. If necessary, the pigments to which each coating layer has been applied can be separated, dried, calcined as necessary and then resuspended to apply additional layers by precipitation.

In addition, the coating may also be carried out by vapor phase coating in a fluidized bed reactor, for example using the techniques proposed for producing pearlescent pigments in EP 0 045 851 and EP 0 106 235 correspondingly. Can be.

The metal oxide with the high refractive index used is preferably titanium dioxide and the metal oxide with the low refractive index used is preferably silicon dioxide.

The method described in US Pat. No. 3,553,001 is preferred when applying the titanium dioxide layer.

The aqueous titanium salt solution is slowly added to the suspension of material to be coated, heated to a temperature of about 50 to 100 ° C., in particular 70 to 80 ° C., and the base is maintained at a substantially constant pH of about 0.5 to 5, especially about 1.5 to 2.5. For example, an aqueous ammonia solution or an aqueous alkali metal hydroxide solution is simultaneously metered in. When the layer thickness of the TiO ₂ precipitation reaches the desired level, the addition of the titanium salt solution and the base is stopped.

This method, also called titration method, is noteworthy in that it avoids excessive addition of titanium salts. This method is achieved by adding only the amount needed to uniformly coat with hydrated TiO ₂ per unit time in hydrolysis and which can be absorbed per unit time by the available surface area of the particles to be coated. Thus, no hydrated titanium dioxide particles are generated that do not precipitate on the surface to be coated.

When applying the silicon dioxide layer, the following method is used. The sodium silicate solution is added metered to a suspension of the material to be coated, heated to 50-100 ° C., in particular 70-80 ° C. The pH is kept constant at 7.5 by the simultaneous addition of 10% hydrochloric acid. When the layer thickness of the SiO ₂ precipitation reaches the desired level, the addition of the silicate solution is stopped. Then stir for 30 minutes.

No method of wet chemical production of interference layers with high refractive index and at least two interference layers with low refractive index with precisely defined thickness and smooth surface on finely divided platelet-shaped supports has ever been disclosed. It should first be noted that the application of metal oxides with low refractive index to the transparent carrier material is essential.

It is also possible to use post-coating or post-treatment methods which make the finished pigments more resistant to light, weather and chemicals, or to facilitate mixing with different media, in particular when handling the pigments. Suitable post-coating and post-treatment methods are described, for example, in German patent C 22 15 191, German patent A 31 51 354, German patent A 32 35 017 or German patent A 33 34 598. Contents.

The applied support constitutes only about 0.1 to 5% by weight, preferably about 0.5 to 3% by weight of the total pigment.

In addition, the novel pigments may also be coated with inorganic or organic colorants which have low solubility and are uniformly fixed. It is preferred to use color lakes, in particular aluminum lake pigments. For this purpose, the aluminum hydroxide layer is applied by precipitation and colored in a second step with the lake pigment. This method is described in detail in German Patent No. 24 29 762 and German Patent No. 29 28 287.

As described in European Patent No. 0 141 173 and German Patent No. 23 13 332, complexing pigments, in particular cyanoferrate complexes (for example, Prussian blue and Turnbull's blue) Further coating is 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 suspension of the pigment is prepared in a dye solution and the dye solution is mixed with a low or zero solubility of the dye.

In addition, metal chalcogenide or metal chalcogenide hydrate and carbon black may also be used when further coating.

The present invention will be described in detail without limiting in the following examples.

Example 1

The circulation belt of polyethylene terephthalate (width: 0.3 m, speed: 20 m / min) is coated with a 20% titanium tetrachloride solution using a reverse spin applicator roll. The coating solution contains 0.3% by weight of surfactant (manufacturer: Daniel Products Company, DISPERSE-AYD W-28). The aqueous film on the belt is exposed to hot air at 70 ° C. to dry in the drying zone and the formed layer is separated from the belt in a separate bath filled with deionized water. Titanium dioxide platelets are filtered and washed with deionized water. The platelets have silver gloss and a coating layer thickness of 100 ± 10 nm.

For further coating, the platelets are redispersed in deionized water or dried at 110 ° C.

Example 2

5-layer system of TiO ₂ / SiO ₂ / TiO ₂ / SiO ₂ / TiO ₂

1) SiO ₂ layer:

50 g of TiO ₂ flakes (particle size <20 μm) with yellow interference color are suspended in 1.5 L of deionized water and the suspension is heated to 75 ° C. 270 mL of sodium silicate solution (125 g of SiO ₂ / L) is added to the suspension at 75 ° C. for 90 min. The pH is kept constant at 7.5 with 10% hydrochloric acid while the sodium silicate solution is added. When the addition is complete, the mixture is stirred at 75 ° C. for 30 minutes to complete the precipitation.

2) TiO ₂ layer:

The pH of the suspension is lowered to 2.2 with 10% hydrochloric acid and 590 ml of TiCl ₄ aqueous solution (400 g of TiCl ₄ / l) is metered in for 3 hours and added. The pH is kept constant at 2.2 with 32% NaOH solution during the addition. When the addition is complete, the mixture is stirred at 75 ° C. for 30 minutes to complete the precipitation.

The mixture is then cooled to room temperature and the pigment obtained is filtered off, then the salt is removed by washing with deionized water and dried at 110 ° C. The pigment is then calcined at 700 ° C. for 30 minutes. The pigment thus obtained exhibits a brighter, goldish interference color that is substantially darker than the color of the initial material.

Example 3

5-layer system of TiO ₂ / SiO ₂ / TiO ₂ / SiO ₂ / TiO _{2 with} blue interference color

1) SiO ₂ layer:

40 g of TiO ₂ flakes with silver interference color are suspended in 1.5 L of deionized water and the suspension is heated to 75 ° C. 580 mL of sodium silicate solution (125 g of SiO ₂ / L) is added to the suspension by metering at 75 ° C. for 180 min. The pH is kept constant at 7.5 with 10% hydrochloric acid while the sodium silicate solution is added. When the addition is complete, the mixture is stirred at 75 ° C. for 30 minutes to complete the precipitation.

2) TiO ₂ layer:

The pH of the suspension is lowered to 2.2 with 10% hydrochloric acid and 470 ml of TiCl ₄ aqueous solution (400 g of TiCl ₄ / l) is metered in for 120 minutes and added. The pH is kept constant at 2.2 with 32% NaOH solution during the addition. When the addition is complete, the mixture is stirred at 75 ° C. for 30 minutes to complete the precipitation.

The mixture is then cooled to room temperature and the pigment obtained is filtered off, then the salt is removed by washing with deionized water and dried at 110 ° C. The pigment is then calcined at 700 ° C. for 30 minutes.

The pigment thus obtained exhibits a dark blue interfering color.

Claims (10)

① solidify and hydrolyze the hydrolyzable titanium compound aqueous solution by heat on the continuous belt, ② separate the coating layer of the produced titanium dioxide, and ③ the titanium dioxide platelet produced in ②, in the presence or absence of the drying step by the wet method. Is alternately coated with a metal oxide hydrate having a high refractive index and a metal oxide hydrate having a low refractive index, ④ hydrolyzing the corresponding water soluble metal compounds, ⑤ the material thus obtained is separated, dried and calcined as necessary A multilayer interference pigment comprising platelet-shaped titanium dioxide as a carrier material, which can be obtained, which is alternately coated with a metal oxide layer having a high refractive index and a metal oxide layer having a low refractive index, having a refractive index difference of at least 0.1. The method of claim 1, Oxides with high refractive index are TiO ₂ , ZrO ₂ , Fe ₂ O ₃ , Fe ₃ O ₄ , Cr ₂ O ₃ , ZnO or mixtures of these oxides or iron titanates, iron oxide hydrates, titanium suboxides or mixtures of these compounds Or an interference pigment, characterized in that it is a mixed phase. The method according to claim 1 or 2, Metal oxides having a low refractive index are SiO ₂ , Al ₂ O ₃ , AlOOH, B ₂ O _3, or mixtures thereof, characterized in that alkali metal oxides and alkaline earth metal oxides may be present as further constituents, if desired Interference pigments. ① applying an aqueous hydrolyzable titanium compound solution to the continuous belt as a thin film; (2) while the titanium dioxide is produced by a chemical reaction in an aqueous solution, the liquid film is dried and solidified; ③ the resulting layer is then separated from the belt and washed; (4) the metal having a high refractive index by suspending the obtained titanium dioxide platelet in water in the presence or absence of a drying step and adding and hydrolyzing water-soluble metal compounds of a metal oxide hydrate having a high refractive index and a metal oxide having a low refractive index. Alternately coating with oxide hydrate and metal oxide hydrate with low refractive index; 5. A process for the preparation of the novel pigments according to any one of claims 1 to 3, characterized in that the coated titanium dioxide platelets are separated from the aqueous suspension, dried and calcined as necessary. The method of claim 4, wherein Oxides with high refractive index are TiO ₂ , ZrO ₂ , Fe ₂ O ₃ , Fe ₃ O ₄ , Cr ₂ O ₃ , ZnO or mixtures of these oxides or iron titanates, iron oxide hydrates, titanium suboxides or mixtures of these compounds Or a mixed phase. The method of claim 4, wherein Metal oxides having a low refractive index are SiO ₂ , Al ₂ O ₃ , AlOOH, B ₂ O _3, or mixtures thereof, characterized in that alkali metal oxides and alkaline earth metal oxides may be present as further constituents, if desired Way. The method according to any one of claims 4 to 6, A method of applying a metal oxide in a fluidized bed reactor by chemical vapor deposition (CVD) followed by intermediate drying of the material to be coated. Use of the pigment according to any one of claims 1 to 3 for coloring paints, printing inks, plastics, cosmetics, agricultural films and glazes for ceramics and glass. The method of claim 8, Use of a pigment as a mixture of commercially available pigments. Paints, printing inks, plastics, cosmetics, agricultural films, ceramics and glass, colored with the pigments according to claim 1.