Deep blue-black effect pigments

Abstract

The present invention relates to effect pigments exhibiting a deep black base color and an interference color of blue, to a process for the production of such pigments and to the use thereof, in particular in coating compositions.

Description

[0001] This application is a divisional application of application number 202080020980.5.

[0002] This invention relates to effect pigments that express a deep black base color and a blue interference color, methods for preparing such pigments, and their uses, particularly in coating compositions.

[0003] The blue-black effect pigments of this invention are particularly useful for decorative and automotive applications, where there is a strong demand for a neutral, deep black body color with high gloss and strong blue interference. Of course, they can also be used in other fields, especially in printing inks, where their color properties (also in combination with any kind of colored pigment), or their additional magnetic properties, may be of interest.

[0004] In addition to colored pigments with attractive hues, there has long been a need for pigments that can absorb deep black and produce high-gloss black. Carbon black pigments have traditionally been used in automotive, decorative, and printing applications; the above are just a few examples.

[0005] Unfortunately, carbon black absorbing pigments do not exhibit any gloss and must be combined with glossy pigments to achieve the glossy black appearance of the corresponding product, thereby reducing the blackness.

[0006] Therefore, there were attempts to replace matte carbon black pigments with glossy black pigments that do not contain carbon black.

[0007] US 3,926,659 discloses mica pigments arbitrarily coated with TiO2 or ZrO2 or their hydrates, having a uniform iron-containing layer on which can be α-iron oxide (hematite, Fe2O3) or magnetite (Fe3O4). The color characteristics of these pigments are largely due to interference colors produced by the TiO2 or ZrO2 layer, which are slightly varied by the α-iron oxide layer applied thereon. Depending on the thickness of the α-iron oxide layer, the main color is a warm reddish-brown hue. If a magnetite layer is prepared on top of the TiO2 or ZrO2 layer, the interference colors produced by the underlying layer are either enhanced by the thin black magnetite layer or superimposed by the thick magnetite layer. Pigments with thick magnetite layers lose their luster because the crystal structure resulting from the corresponding preparation method is said to be coarse.

[0008] This type of pigment cannot meet the requirement of combining strong black absorption color with good hiding power and attractive gloss.

[0009] DE 100 65 761A1 describes sheet-like magnetic particles that are multilayered and contain a core comprising a core of Al₂O₃ or a mixture of Al₂O₂ and SiO₂, an intermediate layer of amorphous SiO₂, and an iron-containing shell, the latter particularly containing magnetite or hematite. These particles are coated with an inorganic or organic coupling agent that reacts with nucleic acids or proteins in aqueous solution to separate them. Because these pigments are prepared from aluminum powder by suspending it in water and adding a water-soluble silicate compound, their core is not a homogeneous composition but a mixed oxide of aluminum and silicon, with the remainder optionally being aluminum metal. Furthermore, because the core material decomposes at least partially, the sheet-like shape and smooth surface of the particles may not be maintained in the resulting pigment. Moreover, controlling this preparation method (aluminothermic process) is difficult because the reaction of aluminum powder in water is itself highly exothermic and because the subsequent reaction with iron compounds is also hazardous. The color properties of these pigments are not described and do not serve their intended purpose.

[0010] DE 3617430 describes flake-shaped colored pigments composed of flake-shaped substrates of mica, glass, metal, or graphite, especially mica, which may be pre-coated with a metal oxide layer and contain a dense Fe(II)-containing layer directly on the substrate or on the metal oxide layer. Additional coating layers are also possible. The Fe(II)-containing layer may be Fe3O4 and is described as dense and compact due to the specific reduction method used to prepare these pigments. The resulting pigment exhibits a black host color in conjunction with interference colors.

[0011] US 7,303,622 discloses a glossy black interference pigment based on a mixture of fine and coarse substrate particles, comprising an Fe3O4 coating, a colorless low-refractive-index coating thereon, and an absorbing high-refractive-index material optionally covering only a portion of the surface thereon, and other layers optionally serving as a protective layer. Mica with a different particle size range (fractions obtained through pigment grading) is used as a preferred substrate. The resulting pigment mixture is said to exhibit a black body color and high gloss. Furthermore, the pigment mixture is said to not produce significant angle-dependent anisochromaticity (angle-dependent interference color).

[0012] Although the pigments described in the latter two prior art documents exhibit a slightly glossy black appearance, there is still a need for a black effect pigment that can represent a neutral deep black body color and has a higher gloss and chromaticity than the pigments in the prior art. This pigment does indeed have an additional blue interference color and good stability in the application medium, does not exhibit any color flop, and can be prepared by an economical method that is easy to control and does not involve reduction steps or high temperatures.

[0013] Therefore, the object of the present invention is to provide pigments that meet the above requirements, do not have the adverse effects of pigments described in the prior art, and can be prepared in a simple wet coating method without involving any reduction step, to provide an economical method for preparing these pigments, and their uses.

[0014] The objective of this invention is achieved through deep blue-black effect pigments, wherein each pigment contains

[0015] - A transparent dielectric sheet-like substrate synthesized from materials possessing green interference color and a refractive index n greater than 1.5, and

[0016] - At least one layered structure on the sheet-like substrate consisting of the following

[0017] ○ The first layer, composed of hematite and / or goethite, and

[0018] ○The second layer, composed of magnetite

[0019] The second layer is located on top of the first layer, and the first layer is located directly on the substrate.

[0020] Furthermore, the objective of this invention is achieved through a method for preparing a deep blue-black effect pigment, which includes the following steps:

[0021] (a) A transparent dielectric sheet-like substrate with a green interference color and a refractive index n greater than 1.5 was dispersed in water.

[0022] (b) Adding a water-soluble iron(III) compound at pH 2 to 4 and maintaining the pH constant, thereby causing a layer of hematite and / or goethite to precipitate onto the surface of the substrate particles.

[0023] (c) Raising the pH to a value between 5.5 and 7.5 and adding water-soluble iron(II) and water-soluble iron(III) compounds, and optionally also adding an aqueous solution of an aluminum compound, while keeping the pH constant, thereby directly precipitating a magnetite layer optionally containing an aluminum compound onto the surface of the substrate particles pre-coated in step (b).

[0024] (d) Optionally wash and filter the resulting product, and

[0025] (e) Dry at a temperature in the range of >100°C to 260°C.

[0026] Furthermore, the object of the present invention is achieved by using the effect pigment in coloring inks, quick-drying paints, oil paints, varnishes, coating compositions, plastics, foils, paper, ceramics, glass, for laser marking, and for preparing coloring pigments with different solvent contents.

[0027] For coating compositions that provide an appealing black color in technical applications, the effect pigments are required to exhibit a deep black body color that is as neutral as possible and an interference color of blue without any green or red hues (confirmed, for example, by very small a* values ​​less than ±1 and as large as possible in the negative range, when measuring the color properties of the applied coating composition). Furthermore, the color characteristics of the effect pigments in the applied state should advantageously be as stable as possible at any measurement angle (i.e., no color-changing effect is observed under varying viewing angles and / or measurement angles).

[0028] Therefore, the inventors faced the challenge of providing effect pigments with a neutral, deep black body color combined with blue interference colors that do not exhibit red or green hues, wherein the pigments must additionally meet the stability requirements for technical applications, particularly the requirement of good chemical and thermal stability.

[0029] Surprisingly, the inventors have indeed discovered that if specific flake-shaped substrate particles are used, the effect pigments, which are essentially composed of the flake-shaped substrate particles and the iron-containing coating surrounding the substrate particles, can exhibit the desired optical properties.

[0030] These specific substrate particles are transparent, synthetically prepared sheet-like substrate particles that inherently possess a green interference color and a refractive index n greater than 1.5.

[0031] A substrate sheet is considered transparent in the sense of this invention if it transmits incident visible light substantially (i.e., to at least 80%). Furthermore, the substrate sheet used according to this invention does not absorb color.

[0032] The substrate sheet utilized according to the present invention is a sheet-like substrate prepared by synthesis with a uniform composition, having an upper surface and a lower surface that form the principal surfaces of the respective sheet and are arranged parallel to each other. In the context of the present invention, parallelism refers not only to geometric parallelism but also to a positioning deviation of up to 15° between the surfaces compared to their geometric parallelism. The length or width of these principal surfaces of the respective substrate sheet represents the grain size of the substrate sheet in its respective longest dimension, while the spacing between the substrate surfaces represents the geometric thickness of the respective substrate sheet.

[0033] Furthermore, the sheet-like substrate prepared according to the present invention has a planar and very smooth surface. Due to the synthetic preparation of the substrate sheet, the surface properties, geometric thickness and thickness distribution, particle size and particle size distribution can be precisely controlled and set by means of process parameters during the preparation of the substrate sheet, which cannot be guaranteed in the case of natural materials such as mica, talc or kaolinite, or even synthetically prepared mica, which are often also used as substrate materials for effect pigments.

[0034] Due to the very flat, parallel surfaces, uniform composition, and lack of color absorption of the substrate sheet, in a clear, transparent medium surrounding it with a refractive index different from that of the sheet, the sheet reflects at least 5% and at most 20%, particularly 6% to 20%, of incident visible light, depending on the corresponding refractive index of the sheet. Here, the higher the refractive index of the corresponding sheet material used, the greater the proportion of light reflected. This reflection at the corresponding interface with the ambient medium, combined with the resulting path difference, leads to monochromatic interference of the reflected beam, and thus to the inherent interference color of the substrate sheet.

[0035] The substrate sheet used in this invention has an inherent green interference color (light in the wavelength range of 490 to 570 nm), which is determined based on diffuse or total reflection of the substrate sheet in a transparent colorless medium.

[0036] To determine this inherent interference color, the Hunter L*,a*,b* diagram is determined by diffuse reflection or total internal reflection of incident visible light measured with the aid of a corresponding Ulbricht sphere (sample: a 10 μm thick coating on a transparent PET film, comprising a commercially available transparent colorless gravure printing adhesive and 10% by weight of a substrate sheet). Here, the reflectance value of the substrate sheet according to the invention is in the Hunter L*,a*,b* diagram in each case in the range of L > 30, particularly L = 40 to 80, b = -20 to +20, particularly -10 to +10, and a < 0, particularly a = -0.1 to -20, particularly preferably -0.1 to -10.

[0037] Traditional pigment substrates lack monochromatic interference colors or exhibit no clearly visible and measurable monochromatic interference colors. Therefore, due to their layered silicate structure and consequently non-planar surfaces, mica flakes, whether based on natural or synthetic mica, cannot inherently exhibit the type of interference that manifests as a uniform, perceptible, dominant, monochromatic interference color. Instead, with relatively large layer thickness distributions, mica shimmers with various colors, resulting in a whitish, indeterminate overall color impression in the case of loose beds of pure mica flakes.

[0038] Provided that the substrate sheet has a planar and parallel substrate surface, the optical properties of the substrate used according to the present invention are substantially determined by the refractive index of the substrate material and the geometric thickness of the substrate.

[0039] Due to the presence of any foreign oxides, but also due to the included porosity or the crystal variant of the preferred metal oxide, the refractive index of the substrate material can, in some cases, be comparable to that of a pure substrate material (bulk material, under standard conditions, for example, made by Landolt- The ideal refractive index (as determined by the method) differs from that of the substrate, meaning that the geometric layer thickness of the substrate must be changed accordingly depending on the preparation conditions and the materials used to achieve the desired interference colors.

[0040] To obtain a substrate thickness suitable for pigment preparation, the refractive index n of the substrate material should be at least greater than 1.5, and preferably at least 1.65. Suitable materials for the substrate are therefore dielectric materials or mixtures of materials, wherein in each case the material or mixture has a refractive index n greater than 1.5, preferably at least 1.65.

[0041] Colorless materials or mixtures of materials are preferred.

[0042] Furthermore, the substrate of the interference pigment according to the present invention must have a refractive index n1, the difference Δn between which is at least 0.1 and more preferably at least 0.2 with respect to the refractive index n2 of the interference layer to be applied to the substrate.

[0043] Therefore, suitable materials for the substrate of the interference pigment according to the invention are, in particular, colorless metal oxides or specific glass materials with a refractive index n in the range of >1.5 to 2.5, especially in the range of 1.65 to 2.5.

[0044] Particularly preferred are substrate sheets composed of Al2O3, Al2O3 and TiO2 comprising at most 5% by weight of the substrate, ZrO2, or TiO2, or substrate sheets containing at least 90% by weight of Al2O3, ZrO2, or TiO2. Here, TiO2 may be anatase or rutile variants.

[0045] Other components of the transparent substrate sheet may be oxides or oxide hydrates of Sn, Si, Ce, Al, Ca, Zn, In, and / or Mg; however, they shall be present in the substrate at most 10% by weight and shall not substantially determine the optical properties of the substrate, particularly the interference colors. In particular, for substrates having at least 90% by weight of Al₂O₃, oxides such as SiO₂, SnO₂, In₂O₃, or ZnO may also be present individually or in combination of two or more of these.

[0046] Suitable substrate materials can also be glass sheets that meet the refractive index requirements. This is especially true for glass sheets containing at most 70% by weight of SiO2. Furthermore, this type of glass material also contains Al2O3, CaO, MgO, B2O3, Na2O, K2O, TiO2, ZnO, BaO, Li2O, ZrO2, Nb2O5, P2O5, and / or PbO in different compositions and proportions. High refractive index glass materials, such as flint glass and heavy flint glass, are preferred.

[0047] Depending on the material used, suitable substrate sheets according to the invention have a geometric thickness in the range of 50 to 600 nm.

[0048] Furthermore, a suitable prerequisite for use as a pigment substrate is that the substrate can be synthesized into a planar sheet of the required layer thickness in each case, which is indeed the case for the material indicated. Moreover, it is extremely advantageous if the pigment substrate used according to the invention is in crystalline form, and particularly preferably in single-crystal form, if applicable.

[0049] In order to obtain the green intrinsic interference of the substrate sheet, the substrate sheet containing Al2O3, or containing Al2O3 and TiO2 in a content of up to 5% by weight of the substrate, and the substrate sheet containing at least 90% by weight of Al2O3 in a proportion of the substrate, have a geometric thickness in the range of 50 to 110 nm, 180 to 260 nm, or 350 to 450 nm.

[0050] A substrate sheet containing TiO2 or containing at least 90% by weight of TiO2 based on the weight of the substrate, according to the invention, has a geometric thickness in the range of 110 to 170 nm or in the range of 240 to 310 nm.

[0051] For a substrate sheet composed of ZrO2 or containing at least 90% by weight of ZrO2 based on the weight of the substrate, the geometric thickness of the substrate is, according to the invention, between 140 and 210 nm or in the range of 260 to 400 nm.

[0052] Glass sheets containing up to 70% by weight of SiO2 have a geometric thickness of 230 to 300 nm or 400 to 470 nm.

[0053] The substrate used is particularly preferably an Al2O3-containing substrate flake, or an Al2O3-containing substrate flake with a content of at most 5% by weight of TiO2 based on the weight of the substrate, both of which are hereinafter referred to as aluminum dioxide flakes, wherein the flakes have a geometric thickness in the range of 50 to 110 nm, 180 to 260 nm, or 350 to 450 nm, preferably in the range of 190 to 230 nm. As described below, these can be prepared in single-crystal form.

[0054] Here, the standard deviation of the thickness of each substrate sheet, calculated as the average thickness of the corresponding substrate, is preferably no greater than 10%. This type of relatively small thickness deviation can be controlled by the corresponding preparation method.

[0055] The particle size of the substrate particles corresponding to the maximum dimension of the substrate is typically 5 to 200 μm, particularly 5 to 150 μm, most preferably 7 to 100 μm, and even more preferably 7 to 50 μm. A D of 12 to 25 μm... 50 The value is preferred. A narrow particle size distribution is particularly advantageous. The particle size distribution can be controlled by grinding methods, by grading methods, or by both, or, in the case of a single-crystal substrate, is a parameter of the preparation method.

[0056] Particle size and its distribution can be determined using a variety of methods commonly used in the art. However, according to the present invention, it is preferable to use laser diffraction in a standard method using a Malvern Mastersizer 3000, APA300 (a product of Malvern Instruments Ltd., UK). The advantage of this method is that it allows for the simultaneous determination of particle size and particle size distribution under standard conditions.

[0057] Furthermore, the particle size and thickness of each particle can be determined with the aid of SEM (scanning electron microscopy) images. In the latter case, the particle size and geometric particle thickness can be determined by direct measurement. To determine the average value, at least 1000 particles are evaluated individually, and the results are averaged. The shape factor of the support sheet, i.e., the ratio of length or width to thickness, is typically 2:1 to 1000:1, particularly 5:1 to 500:1, and very particularly preferably 20:1 to 300:1.

[0058] According to the present invention, the deep blue-black effect pigment has at least a layered structure on the substrate particles, the layered structure consisting of a first layer composed of hematite and / or goethite and a second layer composed of magnetite, wherein the first layer is located directly on top of the substrate and the second layer is located on top of the first layer (i.e., further away from the surface of the substrate particles).

[0059] The layered structure may exist only on the two main surfaces of the substrate, but preferably, the transparent substrate particles are encapsulated in such a way that all outer surfaces of the transparent sheet-like substrate are coated with the hematite / goethite-magnetite layered structure. It goes without saying that the hematite / goethite-magnetite layered structure does not necessarily exhibit the same thickness at every individual point on the substrate surface, and even some smaller surface areas of the substrate may not be perfectly coated with the layered structure, or at least the aforementioned hematite / goethite layer. This limitation is due to technical preparation considerations and does not impair the intent of the invention.

[0060] For the purposes of this invention, the layer composed of hematite and / or goethite is hereinafter referred to as the "hematite layer". Its actual composition depends on the precipitation conditions used to prepare it. For the conditions given in the method according to the invention, it has been revealed that the composition of the hematite layer is preferably pure hematite (αFe₂O₃, iron oxide) or hematite containing goethite (αFeO(OH), hydrated iron oxide). Generally, the goethite content is less than the hematite content.

[0061] The layer composed of magnetite is hereinafter referred to as the "magnetite layer" and, when it is prepared by the method according to the invention, it is composed of pure magnetite (Fe3O4) or magnetite containing a very small amount of maghemite (γFe2O3). In a preferred embodiment, the magnetite layer is composed of pure magnetite containing aluminum compounds or magnetite containing very small amounts of maghemite and aluminum compounds, as explained below.

[0062] For the optical properties of the pigments of this invention, it is crucial that the thickness of the magnetite layer within the layered structure is greater than the thickness of the hematite layer. In fact, the thickness of the magnetite layer is much greater than the thickness of the hematite layer. Typically, the thickness of the magnetite layer within the layered structure is at least 15 times the thickness of the hematite layer.

[0063] The hematite layer is coated onto the substrate particles with a very small thickness, starting from a molecular monolayer and having an upper limit of about 10 nm. Typically, the thickness of the hematite layer is in the range of 0.1 to 10 nm, preferably in the range of 2 to 8 nm. According to the invention, the hematite layer can act as a binder for the magnetite layer on top of the hematite layer to be coated below. Furthermore, if the thickness of the hematite layer is in the range of 2 to 10 nm, it contributes to the absorption and interference colors of the resulting interference pigment.

[0064] Furthermore, for alumina sheets that can be used as substrate particles according to the invention, the outer surface of these particles is often not particularly useful for direct iron oxide coating at relatively low to neutral pH values, as in the case of direct coating of Fe3O4 according to the invention.

[0065] Therefore, a thin hematite layer, which can also be used as a means of activating the surface of the substrate particles, is directly coated onto the substrate because it can be successfully deposited directly onto the alumina sheet and itself provides an activated surface, which is advantageous for the subsequent deposition of the magnetite layer. Furthermore, a very smooth and planar surface of the substrate particles can be maintained by depositing a dense and uniform but ultrathin hematite layer.

[0066] Furthermore, if the underlying substrate contains Al2O3 crystals or is composed of such crystals, the subsequent hematite layer can form crystals with the same structure as those present in the underlying substrate, i.e., a corundum crystal structure, which is advantageous for forming a dense hematite layer. In this case, the growth of the hematite layer on a substrate containing Al2O3 crystals or substantially composed of such crystals is similar to the epitaxial crystal growth process of a crystalline layer on a solid substrate.

[0067] Furthermore, the presence of the hematite layer is advantageous for forming a dense, planar, and substantially crystalline layer of Fe3O4 directly on it through a precipitation process without the use of oxidants.

[0068] Hematite layers may contain small amounts of foreign metal ions different from iron, due to trace amounts in the iron compounds used to prepare hematite layers.

[0069] As is known from existing technology, Fe3O4 layers can be formed in reduction methods using hematite layers as starting materials. Following this reduction method, inhomogeneity of the resulting layer should be expected, as irregular reduction (gradients) may occur across the thickness of the original hematite layer. Furthermore, when using existing precipitation methods, if Fe3O4 is precipitated using Fe(II) compounds in the presence of an oxidant at a relatively high pH (8 to 11), the resulting layer exhibits small crystals and a rather loose crystalline structure of Fe3O4, ultimately leading to a dull pigment.

[0070] Conversely, the pigments according to the invention exhibit a strong gloss and a deep blue-black appearance, which is essentially due to the interference and absorption behavior of the substrate and the magnetite layer, and, as mentioned above, also to some extent due to the interference and absorption behavior of the hematite layer.

[0071] Given that black is considered attractive in coating applications, the only useful interference color for layering that does not adversely affect the attractive appearance of black but is still needed is blue interference, because the impression of deep blue-black is still a valuable impression of black. Therefore, in addition to the absorption color of deep black, the blue interference color of the pigment is also needed, but green or red hues of this blue interference color should be avoided.

[0072] Therefore, not only must the thickness of the substrate particles be adjusted as described above, but also the thickness of the magnetite layer, and shockingly, the thickness of the hematite layer, even though it is so thin that it does not contribute to the interference of the pigment on its own, but only accordingly combines with other layers and the substrate. However, the hematite layer provides yellow / red absorption color, which, combined with the green interference color of the substrate, results in the resulting interference pigment having a neutral black absorption color and ultimately only a blue interference color.

[0073] The magnetite layer of the pigment according to the invention has a layered structure with a thickness ranging from 80 nm to 230 nm, particularly from 80 nm to 150 nm. Its manner of obtaining a relatively strong blue interference color in the resulting pigment is adjusted (by means known in the precipitation methods of magnetite layers).

[0074] The magnetite layer exhibits a dense and crystalline structure. It maintains the smoothness of the substrate particles, ensuring that the magnetite layer itself remains smooth, dense, and planar. It exhibits a high refractive index above 2.0 (approximately 2.4). In addition to the blue interference color, the magnetite layer also imparts a black base color and strong luster to the resulting pigment through its absorption.

[0075] Furthermore, it is preferred that the magnetite layer comprises at least one aluminum compound, preferably alumina and / or alumina hydrate. In this regard, a suitable aluminum compound is added while the magnetite layer is deposited on substrate particles pre-coated with hematite. Useful aluminum compounds are, for example, aluminum sulfate, aluminum chloride, or aluminum nitrate.

[0076] The aluminum content of the magnetite layer contributes to its optical behavior and promotes the subsequent deposition of a dielectric layer (if present) on the magnetite layer.

[0077] In the magnetite coating, the alumina and / or alumina hydrates, as described above, are preferably present in an amount of 0.1 to less than 5% by weight, based on the weight of the magnetite coating. They do not form mixed oxides with the iron component because their content is too small. Instead, they exist in the magnetite coating themselves as alumina and / or alumina hydrates, for example, as Al2O3 or AlOOH.

[0078] In addition to the fact that a subsequent dielectric layer (if present) can be more easily coated onto the magnetite layer when the magnetite layer contains an Al compound, the gloss of the resulting pigment can also be improved by the Al compound.

[0079] Therefore, the embodiments of the present invention disclosed above, wherein the magnetite layer comprises an aluminum compound, are preferred.

[0080] In addition to or as an alternative to aluminum, magnetite layers may also contain trace amounts of foreign metal ions different from iron and aluminum. This is due to trace amounts of iron compounds that can be used to prepare magnetite layers.

[0081] The most preferred embodiment of the present invention is wherein the substrate material of the deep blue-black effect pigment is an alumina sheet as defined above, which has a layered structure as described above, directly on and encapsulating the substrate. Thus, the layered structure consists of a first hematite layer and a second magnetite layer, the second magnetite layer being further away from the substrate surface than the first hematite layer and containing an Al compound as defined above, followed by a colorless dielectric layer on top of the magnetite layer.

[0082] Preferably, at least one colorless dielectric layer is present in the pigment according to the invention, on top of the layered structure of hematite / magnetite. In this case, the dielectric layer, made of a colorless, low-refractive-index dielectric material, is located directly on top of the magnetite layer.

[0083] As materials used for these dielectric layers, dielectric metal oxides or metal oxide hydrates are typically used in this invention. They consist of colorless metal oxides or metal oxide hydrates or mixtures thereof, for example, oxides or hydrates of Sn, Ce, Si, Zr and Al, such as tin oxide, cerium oxide, silicon dioxide, zirconium dioxide, and aluminum dioxide or hydrates thereof.

[0084] Specifically, a layer of silicon oxide and / or silicon oxide hydrate or a layer of tin oxide and / or tin oxide hydrate exists directly on top of the second layer (magnetite layer) of the layered structure as described above. A layer of silicon oxide and / or silicon oxide hydrate is preferred.

[0085] The thickness of the silicon dioxide and / or silicon dioxide hydrate layer, or the thickness of the tin oxide and / or tin oxide hydrate layer, is in the range of 1 to 15 nm, preferably in the range of 1 to 5 μm. In this case, although the desired blue interference color provided by the magnetite layer is slightly reduced, the colorless dielectric layer provides good thermal stability to the resulting interference pigment, which is important when the interference pigment is subjected to any heat treatment at higher temperatures in the application medium (which may be the case in some coating processes). Silica and / or silicon dioxide hydrate are dielectric materials with a dense amorphous structure and are therefore very useful for protecting the underlying magnetite layer, and are therefore preferred to be used.

[0086] Furthermore, the deep blue-black effect pigments according to the invention can be further adapted to their application requirements by applying a so-called post-coating layer different from or beyond the silica / silica hydrate layer. The post-coating layer is typically the outermost coating of the interference pigment and can be composed of inorganic or organic compounds or a mixture containing both inorganic and organic components. In the case of inorganic compounds, dielectric layers can also be used. They are known to impart good dispersibility, lightfastness, etc., to different types of effect pigments and are well known in the art. The thickness of the so-called post-coating layer based on inorganic dielectric compounds is typically less than 20 nm, and particularly 1 to 15 nm, preferably 2 to 10 nm. This type of dielectric layer therefore does not cause any interference to the overall pigment system. Here, extremely thin layers of silica (in this case, in a layered system with other post-coatings), alumina, cerium oxide, and / or tin oxide, etc., are used as a single component or in the form of a mixture. In this regard, several extremely thin dielectric layers of different materials stacked one on top of the other, as described above, are commonly used.

[0087] Of course, the colorless dielectric layer and the layer for improving application properties can be used together in one embodiment of the invention. In particular, the deep blue-black effect pigment as described above, i.e., the pigment consisting of alumina flakes having a layered hematite / goethite-magnetite structure and a silica / silica hydrate layer thereon, can additionally have an inorganic post-coating to impart better application properties in the corresponding application medium.

[0088] In addition to or as a substitute for the inorganic dielectric layer used for post-coating as described above, organic materials (e.g., various organosilanes, organotitanates, organozirconates) may be applied as the outermost coating to the surface of the pigments of the present invention to improve their applicability in different application media. Such coatings are known in the field of effect pigments and their application is therefore within the ordinary skill of those skilled in the art. The so-called “post-treatment” or “post-coating” of the effect pigments with organic or inorganic properties that can be used in this invention as described above can be found in the following documents: EP 0 632 109, US 5,759,255, DE 43 17 019, DE 39 29 423, DE 32 35 017, EP 0 492 223, EP 0 342 533, EP 0268 918, EP 0 141174, EP 0 764 191, WO 98 / 13426 or EP 0 465 805; their contents should be included in this invention by reference.

[0089] Another object of the present invention is a method for preparing the deep blue-black effect pigment as described above, which is reliable, economical, easily controllable, and does not involve a reduction step. Therefore, a method comprising the following steps is applied:

[0090] (a) A transparent dielectric sheet-like substrate, which has a green interference color and a refractive index n greater than 1.5, is dispersed in water.

[0091] (b) Adding a water-soluble iron(III) compound at a pH between 2 and 4 and maintaining a constant pH, thereby causing a layer of hematite and / or goethite to precipitate onto the surface of the substrate particles.

[0092] (c) Raise the pH to a value between 5.5 and 7.5 and add water-soluble iron(II) and water-soluble iron(III) compounds, and optionally also add an aqueous solution of an aluminum compound, while keeping the pH constant, thereby directly precipitating a magnetite layer optionally containing an aluminum compound onto the surface of the substrate particles pre-coated in step (b).

[0093] (d) Optionally wash and filter the resulting product, and

[0094] (e) Dry at a temperature in the range of >100°C to 260°C.

[0095] Suitable substrates for synthesis with an inherent green interference color are those already described above, which are transparent and have a refractive index n in the range of >1.5 to 2.5, and particularly 1.65 to 2.5. Preferably, they are substrate sheets composed of Al2O3, Al2O3 and TiO2 in a content of up to 5% by weight of the substrate, ZrO2, or TiO2, or substrate sheets containing at least 90% by weight of Al2O3, ZrO2, or TiO2 by weight of the substrate. Other components of the transparent substrate sheet may be oxides or oxide hydrates of Sn, Si, Ce, Al, Ca, In, or Zn, however, they may be present in the substrate in a content of up to 10% by weight of the substrate.

[0096] Glass sheets as described above, containing up to 70% by weight of SiO2 and other components, are also suitable.

[0097] Depending on the material, the geometric thickness of the substrate, as described above, must be met in order to obtain the inherent interference color of green in the substrate sheet.

[0098] The sheet-like substrates, as described above and consisting primarily of Al2O3, are preferably prepared by the method described in EP 763 573 A2. These substrates contain a small amount of TiO2, which simplifies subsequent interference layer coating. The alumina sheets prepared by this method are obtained in single-crystal form during a crystal growth process, wherein the grain size of the substrate and its geometric thickness with a standard deviation not exceeding 10% can be controlled by process parameters. The corresponding influencing parameters are known to those skilled in the art. If other foreign oxides are present in addition to or in place of TiO2, the procedure is similar to the method described in EP 763 573 A2, but with the raw materials substituted.

[0099] Substrate sheets consisting entirely or primarily of ZrO2, TiO2, their oxide hydrates, or mixtures thereof can be prepared similarly to the method described in WO93 / 08237. However, substrate sheets prepared similarly to this method should not contain any dissolved or insoluble colorants. They are prepared in a belt process from a correspondingly preferably inorganic precursor material, wherein the precursor is applied to a belt, converted to oxide form or oxide hydrate using acid, cured, and subsequently detached from the belt and optionally calcined. The geometric layer thickness of the substrate sheet is adjusted via the amount of precursor layer applied or the wet layer thickness, which can be very precise and results in a narrow thickness distribution with a variation of up to 10%. The particle size of the substrate sheet must be adjusted via subsequent grinding and grading processes, but this is common in the art.

[0100] Thin glass substrates are available from different suppliers in different thicknesses and qualities, such as borosilicate (ECR) glass sheets with thicknesses ranging from 100 to 500 nm from Glassflake Australia Pty Ltd.

[0101] For coating the above-mentioned sheet-like substrate particles with the layered structure of hematite / magnetite according to the present invention, the following procedure is preferred:

[0102] The substrate particles are suspended in water. Preferably, the suspension is heated to a temperature of 75°C to 85°C. The pH of the resulting suspension is adjusted to a value between 2 and 4 and kept constant. Then, a water-soluble iron(III) compound is slowly metered into the suspension while keeping the pH constant. After the addition of the water-soluble iron(III) compound to precipitate a thin layer of hematite and / or goethite onto the surface of the substrate particles is complete, the pH is raised to a value between 5.5 and 7.5 and kept constant, and water-soluble iron(II) compounds and other water-soluble iron(III) compounds are added to the suspension one by one or in mixture (preferably the latter). Where an aluminum compound is preferably incorporated into the magnetite layer, the pH is preferably adjusted to a value between 6.5 and 7.5 and kept constant. Then, before, after, or preferably simultaneously with the iron(II) and iron(III) compounds, an aqueous solution of the aluminum compound is slowly metered into the suspension while keeping the pH constant. The suspension is preferably maintained under stirring for an additional 0.5 hours, while keeping the pH constant.

[0103] The first and second water-soluble iron(III) compounds can be the same or different compounds. Preferably, the same water-soluble compound is used for both the first and second additions of the iron(III) compound. The amount of the first iron(III) compound added is selected such that only a very thin layer of hematite is deposited on the surface of the substrate particles by using this iron(III) compound. As described above, the resulting layer thickness is in the range of a few molecular layers to about 10 nm. Conversely, the amount of iron(II) compound and the amount of the second iron(III) compound added together with the iron(II) compound are selected in a ratio of iron(II) ions to iron(III) ions between 9:1 and 9.7:0.3, so that magnetite can be directly deposited on the surface of the pre-coated substrate particles. Although there is a large excess of iron(II) compound beforehand, it must be mentioned that the iron(II) compound is partially converted into iron(III) oxide due to process conditions, resulting in the direct precipitation of magnetite.

[0104] Furthermore, the amounts of iron(II) and iron(III) compounds used to produce the magnetite layer are selected such that the thickness of the resulting magnetite layer is greater than the thickness of the hematite layer. Preferably, this amount is selected such that the thickness of the resulting magnetite layer is at least 15 times the thickness of the hematite layer. This is because the density of the hematite layer is very similar to that of the magnetite layer (5.24 g / cm³). 3 With 5.17 g / cm 3 The rule of thumb applies: approximately 5 x 10^6 times. -3 g of hematite or magnetite in 1m 2 Any material with a layer thickness of about 1 nm is coated on the corresponding substrate.

[0105] Typically, the following water-soluble iron compounds can be used: FeSO4, FeCl2, Fe(NH2)2(SO4)2, Fe(NO3)2, Fe2(SO4)3, FeCl3, FeNH4(SO4)2 or Fe(NO3)3; FeSO4 and Fe(NO3)3 are particularly preferred.

[0106] More specifically, FeSO4·7H2O is preferably used as a water-soluble iron(II) compound. Fe(NO3)3·9H2O is preferably used as a water-soluble iron(III) compound. These compounds can be used in industrial-grade form, allowing for the presence of small amounts of non-Fe metal ions.

[0107] As previously stated, the inclusion of an aluminum compound in the magnetite layer is highly advantageous for the interference pigments of this invention. This Al compound improves the convenience of coating the magnetite layer with other dielectric layers as described above and further enhances the stability and density of the magnetite layer. Useful Al compounds are water-soluble Al salts, such as AlCl3 and Al2(SO4)3, particularly AlCl3·6H2O and Al2(SO4)3·16H2O, or polyaluminum chloride solution (PAC). This compound can be simply mixed with the aforementioned iron (II) and iron (III) compounds in suitable proportions and then slowly applied to a suspension of substrate particles that have been pre-coated with a hematite layer. The conditions for adding the Al compound are as described above.

[0108] After the magnetite layer has precipitated, the resulting pigment is separated, optionally washed, and dried. Drying is carried out at temperatures ranging from 100°C to 260°C, particularly from 110°C to 140°C. The drying time is 0.5 to 12 hours.

[0109] Optionally, the resulting pigments can then be graded to further restrict their particle size distribution.

[0110] Preferably, the above method is carried out in an inert gas atmosphere, such as nitrogen or argon.

[0111] In a preferred embodiment of the invention, the deep blue-black effect pigment, on top of the layered structure of hematite / magnetite, i.e., on top of the magnetite layer, comprises at least one colorless dielectric layer that provides the necessary thermal stability to the pigment in the underlying layer.

[0112] In this regard, once the layered structure of hematite / magnetite has been applied to the substrate particles, at least one additional dielectric layer is coated onto the magnetite layer. The coating of these additional dielectric layers is preferably completed before the aforementioned drying step, although an intermediate drying step is also possible. Optionally, washing and / or filtering steps can be performed after each dielectric layer has been coated onto the pre-coated substrate particles.

[0113] The material of the dielectric layer is preferably selected from dielectric metal oxides and / or metal oxide hydrates. Preferably, when only a single dielectric layer is applied to the magnetite layer, this single dielectric layer is preferably composed of a colorless dielectric material with a low refractive index. Most preferably, a single dielectric layer of silicon dioxide and / or silicon oxide hydrate or a single dielectric layer of tin dioxide and / or tin oxide hydrate is applied directly on top of the magnetite layer. Silicon dioxide and / or silicon dioxide hydrate is the most preferred.

[0114] Depending on the thickness of the low-refractive-index dielectric layer on top of the magnetite layer, the blue interference color produced by the underlying pigment can be slightly reduced, but still remains within acceptable limits. The resulting pigment exhibits a deep black body color combined with visible blue interference colors, without any red or green hues, and possesses high hiding power and strong gloss. No angle-dependent interference color (color flop) is observed. Furthermore, the resulting interference pigment exhibits good thermal stability.

[0115] Regarding the formation of a dielectric layer on the magnetite layer of the pigments of the present invention, procedures generally known in the fields of pearlescent and effect pigments can be utilized. Wet chemical coating procedures are preferred, and particularly preferred are wet chemical coating methods using inorganic starting materials, because these methods are easy to operate and control, and inherently result in encapsulated particles.

[0116] Typically, a wet coating method for coating pigment particles with a dielectric layer (particularly a dielectric metal oxide or metal oxide hydrate layer) is performed as follows: The pigment particles are suspended in water, and one or more hydrateable metal salts are added at a pH value selected in a manner suitable for hydrolysis and such that the metal oxide or metal oxide hydrate is directly precipitated to a platelet without any secondary precipitation. The pH value is usually maintained constant by simultaneously metering the addition of alkali and / or acid. Subsequently, the pigment is separated, washed, dried, and sintered (if necessary).

[0117] In the pigment preparation method according to the invention, the sintering step is completely omitted for the layered hematite / magnetite structure and for all dielectric layers coated onto the layered hematite / magnetite structure. This is because the magnetite layer would be damaged by the high temperatures typically used in the sintering step.

[0118] For completeness, the coating of the dielectric layer can also be carried out in a fluidized bed reactor by means of vapor phase coating, in which the techniques for preparing pearlescent pigments proposed in EP 0 045 851 and EP 0 106 235 may be suitably used, for example. However, the wet coating method described above is clearly preferred.

[0119] The coating of pigment particles pre-coated with a layered structure of hematite / goethite-magnetite having a silica layer and / or a silica hydrate layer, using the wet chemical method described above, can be accomplished using the procedure described below: A solution of potassium silicate or sodium silicate is metered into a suspension of the material to be coated and heated to approximately 50-100°C. The pH is maintained constant at approximately 6-9 by simultaneously adding a diluted inorganic acid such as HCl, HNO3, or H2SO4. Once the desired SiO2 layer thickness is reached, the addition of the silicate solution is immediately stopped. The batch is then stirred for approximately 0.5 hours. Depending on whether silica or silica hydrate should be obtained, the drying and / or sintering of the resulting layer is carried out at a medium or higher temperature, preferably at approximately 120°C or higher.

[0120] Next, additional dielectric layers can be applied on top of the first dielectric layer, serving as a further protective layer for the application medium of the pigment and as a so-called post-coating layer, which does not impart or reduce interference colors to the resulting pigment. These inorganic dielectric layers, as well as the organic protective layers that can also be applied thereon, have been described to some extent previously. Corresponding methods are also known in the art.

[0121] The deep blue-black effect pigments of the present invention, possessing the above-described characteristics, are used in application media that particularly rely on deep black and high gloss, especially in automotive applications, general technical coating applications, or printing media. Of course, they can also be used in other applications where black pigments are generally useful.

[0122] Therefore, one object of the present invention is the use of the deep blue-black effect pigment according to the invention in coloring inks, paints, varnishes, coating compositions (i.e., liquid coating compositions and powder coating compositions), plastics, foils, paper, ceramics, glass, for laser marking, and for coloring pigment formulations with different solvent contents.

[0123] Their respective uses in automotive paints, automotive coating compositions and automotive quick-drying paints are particularly preferred.

[0124] Depending on the actual particle size of the deep blue-black interference pigment, printing inks can include all types of printing inks commonly used in printing operations, including inks for screen printing, inks for gravure printing such as intaglio printing, inks for offset printing, inks for flexographic printing, and inkjet printing, to name just a few.

[0125] While applicable to virtually all technical applications requiring highly attractive, saturated blacks, the effect pigments of this invention are most useful in automotive applications, namely automotive paints, automotive coating compositions, and automotive fast-drying paints. In addition to the effect pigments according to the invention, the corresponding compositions also contain at least one binder conventionally used in automotive applications, and optionally at least one solvent.

[0126] Conventional OEM coating compositions used as standard in industry can be used as carriers here. Depending on the coating method and other factors, 1-component solvent-loaded, 2-component solvent-loaded, 1-component water-loaded, or powder formulations are suitable.

[0127] Depending on the chosen coating system, different adhesive systems and crosslinking agents can be used as standards. Typically, acrylate-based / melamine-based adhesive systems, acrylate / melamine / silyl-based adhesive systems, or urethane / melamine-based adhesive systems are useful, but epoxy resins and polyurethanes can also be used.

[0128] The solids content of different solvent-based and water-based coating systems is approximately 40% to 65% in the case of solvent-based systems and approximately 35% to 45% in the case of water-based systems. In the case of powder coatings, the solids content is 100%.

[0129] Automotive paints, quick-drying paints, or coating compositions may, of course, contain conventional adjuvants and additives commonly found in automotive applications. In addition to necessary crosslinking agents, there are also components such as UV absorbers, HALS (hindered amine light stabilizers), and additives for degassing, improving flow behavior, improving scratch resistance, and improving adhesion.

[0130] Automotive paint, quick-drying paint, or coating compositions containing the effect pigments of the present invention are advantageously used in the color-providing base coat of a multilayer coating system. A clear coat is typically applied on top of the base coat.

[0131] The resulting coating including the primer layer can be a single-layer or two-layer primer layer. A single-layer primer layer is preferred. The primer layer contains all the main substances and additives typically used for this purpose, particularly the absorbent pigments for the opaque coating beneath the clear coat. The primer layer also contains the deep blue-black effect pigments of the present invention to provide the vehicle's substrate panel with a saturated black body color that has a high gloss and good hiding power, exhibiting blue interference.

[0132] The substrate panels used for primer coating are automotive body or body parts that have been pretreated in a conventional manner (e.g., e-coating, filler), and are typically composed of metal, plastic, or composite materials. These are provided with a primer coating in a known manner using conventional means and equipment.

[0133] Generally, the pigments of the present invention can be applied to any product that can utilize one of the characteristics of the pigments of the present invention, namely their color properties or the magnetic properties they also exhibit, or both.

[0134] It goes without saying that the deep blue-black effect pigment according to the invention can be used in combination with organic and inorganic colorants, and particularly with any kind of effect pigment. Organic pigments and colorants are, for example, monoazo pigments, diazo pigments, polycyclic pigments, cationic, anionic, or nonionic colorants. Inorganic colorants and pigments are, for example, white pigments, colored pigments, other black pigments, or effect pigments. Examples of suitable effect pigments are metallic effect pigments, pearlescent pigments, or interference pigments, which are typically based on single or multiple coated flakes of aluminum, mica, glass, Al2O3, Fe2O3, SiO2, etc. Examples of the structure and particular characteristics of these pigments are disclosed in particular in RD 471001 or RD 472005, the disclosures of which should be incorporated herein by reference.

[0135] In addition, other colorants that can be used in conjunction with the deep blue-black effect pigment of the present invention are luminescent colorants and / or any type of pigment, as well as holographic pigments or LCPs (liquid crystal polymer-based pigments).

[0136] The pigments according to the invention can be used in any desired mixing ratio with commonly used and commercially available pigments and fillers. Limitations on the use of the pigments of the invention with other pigments and colorants are set only if any mixture would interfere with or limit the color properties of the pigments according to the invention.

[0137] The effect pigments according to the invention provide a neutral, deep black body color and a desired blue interference color for the corresponding application medium. Furthermore, they are glossy, exhibit good hiding power, and, when provided with a suitable protective layer, also exhibit good temperature stability without sacrificing the desired blue interference color. Moreover, the blue interference color is not compromised by red or green interference effects. Based on their valuable color properties, they can be used in all applicable application media.

[0138] The present invention is described in more detail in the following embodiments, but should not be limited thereto.

[0139] Example 1:

[0140] 140 g of alumina flakes (Al₂O₃ with a small amount of TiO₂, average thickness 220 nm, average particle size 18 μm, inherent green interference color) were suspended in deionized water. The suspension was heated to 80 °C while stirring. Nitrogen gas was slowly added to the reaction vessel. The pH was adjusted and maintained constant at 3.0 by metering an acidic compound (HCl, approximately 20 wt%) into the suspension. While maintaining a constant pH, a Fe(NO₃)₃ solution (100 ml, 7.87 g of Fe(NO₃)₃*9H₂O in 140 ml of deionized water) was added to the suspension. The pH was then raised to approximately 7.0 by adding an alkaline composition (NaOH, approximately 32 wt%) to the suspension. While maintaining a constant pH, aqueous solutions of Al, Fe(II), and Fe(III) components (2000 ml, 768.9 g of FeSO4·7H2O, 0.66 g of AlCl3·6H2O, and 24.3 g of Fe(NO3)3·9H2O in 2000 ml of deionized water) were slowly and metered into the suspension. The suspension was then maintained for 30 minutes with stirring. Afterward, water glass solution (approximately 5.9 g, 29% SiO2) was added, while maintaining a constant pH. The suspension was maintained for approximately 2 hours, and then the resulting pigments were separated by filtration and washed with deionized water.

[0141] Finally, the resulting pigment was dried at approximately 120°C and sieved.

[0142] The resulting pigment exhibits a deep blue-black powder color with a bright luster and high hiding power.

[0143] Example 2:

[0144] To illustrate the effect of the thickness (and therefore the inherent interference color) of the flake-like pigment substrate, alumina substrate particles of varying thicknesses were coated with a layered system of hematite / goethite-magnetite according to the procedure disclosed in Example 1 to obtain different interference pigments. The substrates had average thicknesses of 300, 220, and 150 nm, respectively, with only the substrate particles having an average thickness of 220 nm exhibiting the inherent green interference color.

[0145] Three polymer plates pre-coated with a 15 μm thick carbon black-containing coating were sprayed with a coating composition containing, in each case, 10 parts by weight of an acrylic-melamine resin as a binder, 1 part by weight of various interference pigments exhibiting different substrate thicknesses as described above, and 13 parts by weight of a solvent mixture. If necessary, the viscosity of the coating composition was further adjusted for spray application by adding additional solvent. The coating composition was applied to the pre-coated polymer plates to a dry thickness of 15 μm using a commercially available spray gun. Subsequently, a clear topcoat, essentially composed of acrylic-melamine resin (applied in solvent form by spray application), was applied to the layer containing the interference pigments to a dry thickness of 30 μm. Each coated test plate was heat-treated at 140°C for 20 minutes.

[0146] The test panels were evaluated visually and by measuring color data. The corresponding L*a*b* data measured using a BYK-mac i (a spectrophotometer from BYK-Gardner GmbH) are disclosed in Table 1.

[0147] Table 1

[0148] 300 15 42.8 -1.8 -4.3 4.7 254.7 300 25 19.5 -0.2 -4.1 4.2 266.8 300 45 5.4 0.1 -4.9 4.9 270.6 220 15 43.4 -0.2 -11.3 11.3 268.9 220 25 20.6 0.1 -7.4 7.4 270.8 220 45 4.9 0.2 -5.1 5.1 272.6 150 15 45.2 -3.4 -4.3 5.5 231.7 150 25 24.9 -1.9 -3.7 4.1 243.1 150 45 6.5 -0.5 -4.0 4.0 263.3

[0149] According to the color characteristics in Table 1, for the deep blue-black effect pigment of the present invention on a flake-shaped substrate with an inherent green interference color only, the color angle h° remains stable at different measurement angles, the blue interference is strong (negative b* value) and the red or green hues of the interference color cannot be observed (very small a* value).

[0150] Example 3:

[0151] Temperature stability test

[0152] Pigment samples were prepared according to Example 1, provided that the following conditions were met:

[0153] Example 3a: It has only a layered structure of hematite / goethite-magnetite, without a dielectric layer;

[0154] Example 3b: has a layered structure of hematite / goethite-magnetite, and a dielectric layer of SiO2 and / or silica hydrate;

[0155] Example 3c: A layered structure of hematite / goethite-magnetite, with a dielectric layer of SiO2 and / or silica hydrate plus a standard post-coating.

[0156] Example 3d: Mica with a magnetite layer, comparative example

[0157] Store 2g of each pigment at 180°C for 14 hours.

[0158] Store 2g of each pigment at 250°C for 14 hours.

[0159] 1.2 g of each pigment according to Examples 3a to 3d was dry-mixed with 30.0 g of a commercially available powdered varnish composition after storage. The colored powdered coating composition was then applied to a black / white metal test panel using a corona-charged powder spray gun. In each case, the resulting coating was cured at 180°C for 15 minutes.

[0160] After curing, the panels were characterized visually and by measuring the corresponding L*a*b* values ​​using a BYK-mac i spectrophotometer. Using the obtained data, the mDE* values ​​were measured on both black and white surfaces of the test panels. The results are presented in Table 2.

[0161] Table 2

[0162] 180℃ 250℃ 180℃ 250℃ Example 3a 7 28.5 4 16 Example 3b 2 14.5 1 3.5 Example 3c 2 3 2.5 2.5 Example 3d 9 27 7 22

[0163] The results disclosed in Table 2 show that the dielectric layer of SiO2 and / or silica hydrate on top of the layered structure of the hematite / goethite-magnetite effect pigment according to the present invention significantly improves the temperature stability of the pigment. The temperature stability can be further improved by applying a standard post-coating in addition to the dielectric layer of SiO2 and / or silica hydrate.

Claims

1. Deep blue-black effect pigments, each containing... - A transparent dielectric sheet-like substrate synthesized from materials that possess green interference color and a refractive index n greater than 1.

5. - At least one layered structure on the sheet-like substrate consisting of the following: ○ The first layer, composed of hematite and / or goethite, and ○ The second layer, composed of magnetite The second layer is located on top of the first layer, and the first layer is located directly on the substrate. The transparent dielectric sheet-like substrate is a glass sheet having a SiO2 content of up to 70% by weight, or the transparent dielectric sheet-like substrate is composed of Al2O3, composed of Al2O3 and TiO2 with a content of up to 5% by weight based on the weight of the substrate, composed of ZrO2, or composed of TiO2, or wherein the transparent dielectric sheet-like substrate contains at least 90% by weight of Al2O3, ZrO2, or TiO2 based on the weight of the substrate. The sheet-like substrate has a particle size in the range of 5 μm to 200 μm; The first layer has a geometric thickness of 8 to 10 nm; The second layer has a geometric thickness of 80 to 230 nm; and The effect pigment mentioned is a deep blue-black effect pigment.

2. The effect pigment according to claim 1, wherein the transparent dielectric substrate is composed of Al2O3, or of Al2O3 and TiO2 in a content of up to 5% by weight of the substrate, and has a geometric thickness in the range of 50 to 110 nm.

3. The effect pigment according to claim 1, wherein the flake-like substrate has a particle size in the range of 7 to 50 μm.

4. The effect pigment according to claim 1, wherein the second layer has a geometric thickness in the range of 80 to 150 nm.

5. The effect pigment of claim 1, wherein the second layer comprises an aluminum compound.

6. The effect pigment according to claim 1, further comprising a colorless dielectric layer on top of the second layer.

7. The effect pigment according to claim 6, wherein the colorless dielectric layer is a layer of silicon dioxide and / or silicon dioxide hydrate.

8. The effect pigment according to claim 1, comprising an outermost inorganic and / or organic post-coating.

9. The effect pigment according to claim 1, wherein the transparent dielectric substrate is composed of Al2O3, or of Al2O3 and TiO2 in a content of up to 5% by weight of the substrate, and has a geometric thickness in the range of 180 to 260 nm.

10. The effect pigment according to claim 1, wherein the transparent dielectric substrate is composed of Al2O3, or of Al2O3 and TiO2 in a content of up to 5% by weight of the substrate, and has a geometric thickness in the range of 350 to 450 nm.

11. The use of the effect pigment according to any one of claims 1 to 10 in coloring inks, quick-drying paints, oil paints, varnishes, coating compositions, plastics, foils, paper, ceramics, glass, for laser marking, and for coloring pigment formulations with different solvent contents.

12. The use according to claim 11, wherein the quick-drying paint, varnish, or coating composition is an automotive quick-drying paint, automotive varnish, or automotive coating composition.

13. A method for preparing a deep blue-black effect pigment according to any one of claims 1 to 10, comprising the following steps: (a) A transparent dielectric sheet-like substrate, which has a green interference color and a refractive index n greater than 1.5, is dispersed in water. (b) A water-soluble iron(III) compound is added at a pH of 2 to 4 while the pH is kept constant, thereby causing a layer composed of hematite and / or goethite to precipitate onto the surface of the substrate particles. (c) Raise the pH to a value of 5.5 to 7.5 and add water-soluble iron(II) and water-soluble iron(III) compounds, and optionally also add an aqueous solution of an aluminum compound, while keeping the pH constant, thereby directly precipitating a magnetite layer optionally containing an aluminum compound onto the surface of the substrate particles pre-coated in step (b). (d) Optionally wash and filter the resulting product, and (e) Dry at a temperature in the range of >100°C to 260°C.

14. The method of claim 13, wherein the transparent dielectric substrate is composed of Al2O3 or of Al2O3 and TiO2 in a content of up to 5% by weight of the substrate, and has a geometric thickness in the range of 50 to 110 nm, in the range of 180 to 250 nm, or in the range of 350 to 450 nm.

15. The method of claim 13, wherein it is carried out in an inert gas atmosphere.

16. The method of claim 13, wherein, after step (c) and before step (e), in a further step, a colorless dielectric layer is coated onto the magnetite layer.

17. The method of claim 16, wherein the colorless dielectric layer coated onto the magnetite layer is a layer of silicon dioxide and / or silicon oxide hydrate.

18. The method of claim 13, wherein the layer composed of magnetite is applied to the substrate particles with a thickness greater than that of the layer composed of hematite and / or goethite.

19. Deep blue-black effect pigments, each containing [missing information - likely ingredients]. - A transparent dielectric sheet-like substrate synthesized from materials that possess green interference color and a refractive index n greater than 1.

5. - At least one layered structure on the sheet-like substrate consisting of the following: ○ The first layer, composed of hematite and / or goethite, and ○ The second layer, composed of magnetite The second layer is located on top of the first layer, and the first layer is located directly on the substrate. The transparent dielectric sheet-like substrate is a glass sheet having a SiO2 content of up to 70% by weight, or the transparent dielectric sheet-like substrate is composed of Al2O3, composed of Al2O3 and TiO2 with a content of up to 5% by weight based on the weight of the substrate, composed of ZrO2, or composed of TiO2, or wherein the transparent dielectric sheet-like substrate contains at least 90% by weight of Al2O3, ZrO2, or TiO2 based on the weight of the substrate. The sheet-like substrate has a particle size in the range of 5 μm to 200 μm; The first layer has a geometric thickness of 6 to 10 nm; The second layer has a geometric thickness of 80 to 230 nm; and The effect pigment mentioned is a deep blue-black effect pigment.