Radar-compatible coating containing metallic effect pigments on a substrate.

Abstract

The present invention relates to radar-compatible coatings containing metallic effect pigments on substrates, to methods for producing such coatings, and to the use of substrates coated in such methods, particularly in vehicle construction.

Description

[Technical Field]

[0001] The present invention relates to radar-compatible coatings comprising metallic effect pigments on a substrate, methods for producing such coatings, and the use of substrates coated by such method, particularly in vehicle construction. [Background technology]

[0002] With the increasing number of autonomous vehicles, there is an unprecedented need to integrate radar devices into corresponding automotive components that can both measure the distance to other vehicles or obstacles and measure the speed of other road users. Such radar devices are typically installed behind the vehicle's bumper to avoid compromising the vehicle's appearance. For many years, metallic paints, preferably silver metallic paints, have been among the most popular automotive paints, particularly in the passenger car sector. However, conventional metallic paints contain aluminum-based metallic effect pigments that can reflect, attenuate, or absorb radar waves (typically in the 76-81 GHz frequency range). This can be so pronounced that the conventional use of metallic automotive paints for radar system cover components in vehicles can lead to undesirable degradation of the radar system's functionality. Therefore, these metallic paints present significant challenges in the optimal design of radar system cover components installed inside such vehicles. Therefore, considerable effort has been made to provide solutions for covering vehicle radar systems that do not detract from the vehicle's appearance while enabling the excellent functionality of the installed radar system. Therefore, the corresponding cover component is designed, for example, as a radiator grille having a region that transmits radar waves quite substantially and metallized struts that attenuate the radar wave transmission capability only slightly. Such cover components are described, for example, in German Patent Invention No. 19844021 (C2). In the above specification, the visible metal layer on the outside is composed of a vapor-deposited indium layer having a thickness in the nanometer range. It is claimed that the visual appearance of the radiator grille strut thus coated is equivalent to that of chrome plating.

[0003] For example, it is also possible to provide a company emblem using this type of extremely thin sputtered metal layer, as described in European Patent No. 954052 (B1). On the other hand, in German Patent Application Publication No. 102011016683 (A1), a black plastic substrate is coated with a silicon layer with a thickness in the nanometer range. The cover components described above are radiator grilles or company emblems intended to have an appearance equivalent to chrome gloss in certain areas. However, this type of coating is not suitable for vehicle parts located within the beam path of radar equipment but not intended to leave the observer with the visual impression of conventional silver or colored metallic paint. The challenges here lie in achieving the strong brightness flop (a clear change from light to dark when the illumination or observation angle changes) typical of metallic paints, achieving the opacity of metallic paint, and reducing radar wave attenuation to a degree sufficient to allow the radar equipment on which the radar waves are transmitted to operate in a fully functional manner. Japanese Patent Publication No. 2004-244516 discloses a glossy product having high transmittance to electromagnetic radiation that can be used as a radiator grille, but can also be used as a component of another vehicle part, such as a tailgate. The layer on the polycarbonate panel may contain metal particles such as zinc, tin, or indium, but may not, and may be colored with interference pigments such as titanium dioxide-coated mica. The particles are applied to the panel in a polyurethane-containing layer at a concentration of 3 to 8% by mass. A black base coat is applied as a back coating. The resulting lustrous product, which includes multiple layers, is claimed to have high transmittance to electromagnetic radiation and high luster. Excellent penetration against radar radiation can be achieved using interference pigments containing titanium dioxide-coated mica in such coatings, but the opacity of metallic finishes and the strong metallic brightness flop achievable with the latter cannot be obtained with such mica-based interference pigments that have only a simple structure. Japanese Patent Publication No. 2010-030075 therefore proposes a layer having a low concentration of aluminum pigment in addition to glass flakes or titanium dioxide-coated mica on a plastic substrate, which can be used, for example, in a vehicle bumper. It is argued that the low concentration of aluminum pigment in this layer, and the resulting relatively large distances that can be achieved between individual aluminum pigment particles, result in good radar transmittance and high gloss simultaneously. However, the aluminum pigment present in only small amounts cannot achieve the opacity typically obtained from metallic paints, and the glass flakes or TiO2 mica pigment have virtually no opacity. German Patent Application Publication No. 102019209893 (A1) also discloses a radar-transparent coating for vehicle parts (e.g., radiator grilles) comprising a mixture of an aluminum pigment and a silicate pigment in a layer on a plastic substrate. The latter pigment may be titanium dioxide-coated mica or titanium dioxide-coated glass. A second layer located beneath this layer on the substrate is low in brightness and preferably black. The resulting radiator grille has a pearlescent white color and therefore a metallic appearance. However, the visual impression of a metallic finish cannot be achieved with this type of layer structure. [Overview of the project]

[0004] The object of the present invention is to provide a radar wave-transmitting coating on a substrate, which is particularly suitable for use on cover components of radar devices in vehicle construction, and which contains conventional metallic effect pigments, especially aluminum pigments, and preferably has as little visual difference as possible from conventional vehicle metallic finishes, and in particular has a metallic appearance, high opacity and strong brightness flop, while simultaneously having good radar wave transmittance. A further object of the present invention is to provide a method for manufacturing the above-described coating. Furthermore, a further object of the present invention is to demonstrate the use of this type of coating.

[0005] The object of the present invention is achieved by a radar-compatible coating comprising a metallic effect pigment on a substrate, the coating being - A layer (A) containing at least one pigment having absorption properties and not containing a metallic effect pigment, - A layer (B) containing a flake-like effect pigment, wherein the flake-like effect pigment is exclusively a metallic effect pigment, and layer (B) has a layer thickness in the range of 2 to ≤ 10 μm, and layer (B) It has at least one layer package consisting of the following. Furthermore, the object of the present invention can also be achieved by a method for manufacturing a radar-compatible coating containing a metal effect pigment on a substrate, in which, - A layer (A) containing at least one pigment having absorption properties and not containing a metallic effect pigment is applied to an optionally pre-coated substrate, including a plastic plate or plastic film, and thereafter - A layer (B) containing a flake-like effect pigment, wherein the flake-like effect pigment is exclusively a metallic effect pigment, and layer (B) has a dry layer thickness in the range of 2 to ≤ 10 μm, and layer (B) is applied to layer (A). or - A layer (B) containing a flake-like effect pigment, wherein the flake-like effect pigment is exclusively a metallic effect pigment, and layer (B) has a dry layer thickness in the range of 2 to ≤ 10 μm, and layer (B) is applied to an optionally pre-coated substrate including a plastic plate or plastic film, and thereafter - Contains at least one pigment having absorption properties, -A layer (A), which does not contain metallic effect pigments, is applied to layer (B). Furthermore, the objective of the present invention can also be achieved by using the above-mentioned coating on a substrate as a radar-compatible vehicle finish for vehicle components.

[0006] The inventors have surprisingly found that, in contrast to solutions described in prior art literature, a coating having a layer containing flake-like effect pigments, wherein the flake-like effect pigments consist exclusively of metallic effect pigments, can be used to provide cover components for radar devices in vehicle construction. Thus, this type of layer is very similar to conventional metallic finish layers. However, special care must be taken to achieve sufficiently high radar wave transmission necessary for the proper operation of the radar device. Therefore, for example, the coating layer containing metallic effect pigments must have only a low layer thickness. According to the present invention, this is in the range of 2 to ≤10 μm. Within this layer thickness range, a preferred range can be set by selecting the concentration of metallic effect pigments in the coating composition used. Thus, when the proportion of metallic effect pigments in the coating composition is relatively high, a layer thickness in the range of 4 to 7 μm is preferably sufficient, but when the concentration of metallic effect pigments in the coating composition is relatively low, a layer thickness in the range of >7 to <10 μm is more advantageous. Needless to say, variations in layer thickness within the layer as a result of processing techniques should not affect the examples of layer thickness ranges shown here. The decisive factor is the target average layer thickness for each coating operation. However, for the desired functional mode of the coating, it is particularly important that this layer containing the metallic effect pigment is part of a layer package located on a suitable substrate. The layer colored with a metallic effect pigment is referred to herein as layer (B) of the layer package. Layer (B) is located directly above layer (A) on the substrate as viewed from the substrate, but it can also be located directly below layer (A) as viewed from the substrate. In either variation, excellent radar wave transmission of the coating on the substrate can be achieved, but these two variations differ in appearance. Accordingly, the layered package according to the present invention consists of layer (A) and layer (B) on a substrate, and in the first embodiment, layer (B) is located directly above layer (A), and as a result represents the outermost layer of the layered package on the substrate. Alternatively, in the second embodiment, layer (A) is located directly above layer (B), and as a result represents the outermost layer of the layered package on the substrate.

[0007] According to the present invention, layer (A) of the layer package contains at least one (one type) of absorbent pigment. This may be an organic absorbent pigment, an inorganic absorbent pigment, and / or a flake-type effect pigment having absorbent properties. The absorbent pigment may be present in layer (A) individually, as a mixture within one material classification (e.g., as a mixture of various inorganic or organic absorbent pigments), as a mixture from different material classifications (e.g., as a mixture of a flake-type effect pigment having absorbent properties and an organic and / or inorganic absorbent pigment), or as a mixture of an organic and / or inorganic absorbent pigment and a flake-type, non-metallic effect pigment that does not have absorbent properties. Preferably, layer (A) contains at least one flake-type effect pigment having absorbent properties (one type), and organic absorbent pigments and / or inorganic absorbent pigments may be present in the same manner at an optional rate. It is essential to the present invention that the flake-type effect pigment having absorbent properties present in layer (A) cannot be a metallic effect pigment. The organic or inorganic pigments with absorption properties used can be any absorption pigment commonly used in various industrial coatings. These pigments are preferably present with particle diameters in the range of 10 to 500 nm, particularly 10 to <100 nm. Regardless of whether the additionally used absorption pigment is organic or inorganic, when combined with a flake-like effect pigment, if it has a small particle diameter that transmits incident light, the special effects (gloss, brilliance, interference color, etc.) produce particularly excellent visual effects. In such cases, the particle diameter of the absorption pigment is preferably in the range of 10 to <40 nm. Preparations of absorption pigments are generally commercially available. Depending on compatibility with the coating system used, other systems such as Heucotint®W (Heubach, Germany), Heucotint®UN (Heubach, Germany), MIPA WBC (Mipa, Germany), Standoblue® (Standox GmbH, Germany), Standohyd® (Standox GmbH, Germany), Vocaflex® (Arichemie, Germany), Vocaplast® (Arichemie, Germany), or other systems may also be considered. Suitable absorbent pigments include, for example, isoindolidone, benzimidazole, quinacridone, phthalocyanine Cu, perylene, carbon black, and / or titanium dioxide. Preferably, suitable for use in the coating according to the present invention (in this case, in layer (A)) are inorganic and organic absorbing pigments individually or in mixtures, inorganic and / or organic absorbing pigments in mixtures with non-metallic flake-like effect pigments that do not have absorbing properties, or flake-like effect pigments having absorbing properties in mixtures with organic and / or inorganic absorbing pigments (optionally). In a preferred embodiment, layer (A) of the coating layer package according to the present invention is a flake-like effect pigment having absorption properties. In particular, flake-shaped interference pigments having absorption properties are used in accordance with the present invention.

[0008] The optical effects of flaky interference pigments generally result from a combination of light reflection and transmission phenomena in the arrangement of thin layers contained in this type of effect pigment (usually on a flaky support). Quite frequently, only materials that are colorless and substantially transparent to visible light, such as flaky mica pigments coated with titanium dioxide, are used. Such pigments can have silver interference colors or can also have colored interference colors, but are overall transparent and have no masstone. Such pigments can only be used in layer (A) of the coating according to the invention in combination with organic and / or inorganic absorption pigments. When at least one of the flaky support or the layer located on the flaky support consists of a material having a unique color, i.e., an absorption color, the interference pigment acquires absorption characteristics (and thus a masstone). These can be colored metal oxides, metal suboxides, mixed metal oxides, or oxygen-deficient metal oxides or metal oxide hydrates. Interference pigments also acquire absorption characteristics by a layer containing an organic coloring pigment. In addition, suitable pigments are so-called carbon-containing pigments, which contain a certain proportion of elemental carbon in at least one layer consisting of flaky interference pigments. Particularly preferably, it is also possible to use an interference pigment having one or more interference layers on a transparent support flake and, as a final layer, an extremely thin light transmission layer made of carbon. Such pigments are described, for example, in the specification of European Patent Publication No. 3795645 (A1) by the present patent owner.

[0009] The flaky effect pigment having absorption characteristics, preferably used according to the invention, is an interference pigment having at least one layer containing iron oxide such as Fe2O3, FeO, Fe3O4, FeOOH, titanium suboxide such as TiO, Ti2O3, Ti3O5, Ti4O7, Ti2O, Ti3O or Ti6O, or chromium oxide such as Cr2O3, or a layer made of carbon. The flaky support materials to be considered are natural or synthetic mica, kaolin, talc or sericite, or also glass, calcium aluminum borosilicate, SiO2, TiO2, Al2O3, graphite flakes or iron oxide flakes. The flaky support material used is preferably natural or synthetic mica, calcium aluminum borosilicate flakes, glass flakes, SiO2 flakes or Al2O3 flakes. Interference pigments showing colored interference colors and colored absorption colors can be easily used in layer (A). Therefore, for example, the interference pigment sold under the trade name Colorstream® F10-51 Lava Red by Merck KGaA (Darmstadt) has proven to be a particularly suitable colored interference pigment. This pigment is based on a flaky SiO2 substrate and is coated with Fe2O3. Particularly preferably, an interference pigment having a silver-white absorption color is used. Such interference pigments are available, for example, from Merck KGaA under the trade names Iriodin® 9602 Silver-Grey SW, Iriodin® 9605 Blue Shade Silver SW and Iriodin® 9612 Silver-Grey Fine Satin SW. These are based on mica flakes and have at least one layer containing Fe2O3 or titanium oxide. Interference pigments having an absorption color, particularly a silver-white absorption color, can also be used, as already described above, in mixtures with other pigments having absorption properties, for example mixtures with carbon black.

[0010] Interference pigments with a silvery-white absorption color have been found to be particularly suitable for use as pigments with absorption properties in layer (A) when the coating is intended to have an overall silver metallic appearance. Due to the pigment structure, which is in the form of a thin layer arrangement on a flake-like substrate, this type of interference pigment exhibits a visually recognizable gloss when incident light strikes the pigment. Layer (B) contains a metallic effect pigment, and because of its very low thickness, its opacity alone is insufficient to obtain the overall visual impression of an opaque silver metallic finish. Therefore, the opacity of layer (B) is effectively supplemented by the opacity of the pigment with absorption properties in layer (A), especially when an interference pigment with a silvery-white absorption color is present. When layer (B) contains a silver metallic effect pigment, such as a silver aluminum pigment, the silvery-white absorption color of the interference pigment ensures that layers (A) and (B) of the layer package are in the same color region, and that the coating formed by the layer package leaves an essentially homogeneous silver metallic impression with high opacity, high gloss, and a clear lightness flop.

[0011] The opaque silver appearance of the entire coating layer package occurs in both the case of a layer (A)-(B) arrangement relative to the substrate and the case of a layer (B)-(A) arrangement. The gloss and brightness flop of the coating that can be achieved with the layer arrangement (A)-(B) are more pronounced than with the layer arrangement (B)-(A). On the other hand, the radar performance of the two embodiments described above is of the same order. Therefore, in order to achieve the overall silver impression of the layered package, layer (A) of the layered package contains a pigment with absorption properties, and its type and amount are such that when layer (A) is considered individually, it has a gray hue and is therefore achromatic, in the medium lightness range (L * a * b * In the color space, L on a black background * The success of the present invention is particularly advantageous when the type and quantity of 15° are in the range of 40 to 90. *The method for determining the 15 values is described in the Examples section. For this purpose, it has proven to be highly suitable to color the layer (A) with interference pigments having a silver-white absorption color. Inorganic or organic absorption pigments preferably have an achromatic absorption color and may additionally be present in the first layer. Absorption pigments having a chromatic absorption color, particularly interference pigments having a chromatic absorption color, can also be used in layer (A) to increase the hiding power of layer (B). In the layer arrangement (A)-(B) on the substrate, the overall appearance of the layer package varies depending on the metallic effect pigment used. In the case of a silver-colored metallic effect pigment in layer (B), a slight color shift of the overall silver metallic impression in the direction of the absorption color of the interference pigment having a chromatic absorption color occurs, which may be desirable as a specific color nuance. In contrast, when a colored metallic effect pigment in layer (B) is combined with an interference pigment having an absorption color in the same color region (e.g., the orange or red region), a saturated and distinct metallic effect can be achieved in layer (A). In the case of the layer arrangement (B)-(A) on the substrate, such a metallic effect having a saturated color already occurs when using a silver-colored metallic effect pigment in layer (B). As a result, the recognizable color of the entire coating corresponds to the absorption color of the non-metallic interference pigment when no further coloring pigment is present in layer (A). According to the present invention, layer (A) contains a pigment having a chromatic absorption color, and the lightness L * at 15° (L * a * b * in the color space) is in the range of 50 to 100 (measurement conditions in the Examples section). In contrast, layer (A) of the layer package having a black appearance by containing a pigment having absorption characteristics is quite unsuitable for the coating according to the present invention because the overall appearance of the coating caused by the low layer thickness of layer (B) in the layer arrangement (A)-(B) has a cloudy or mottled nature. Even in the case of the layer arrangement (B)-(A), a non-uniform appearance is considered to be obtained. Therefore, a layer (A) having a black color is not preferred according to the present invention. The total concentration of the absorbent pigment in layer (A) is in the range of 10 to 25% by mass, preferably 15 to 20% by mass, based on the mass of layer (A). When an interference pigment with absorption properties is used in the first layer, the interference pigment generally has a particle size in the range of 1 to 100 μm, particularly 2 to 70 μm, and especially preferably 3 to 50 μm. The thickness of the interference pigment is in the range of 0.1 to 2 μm. In contrast, classical absorbing pigments can be organic or inorganic in nature and have particle diameters in the range of about 10 to <100 nm, preferably 1 to <40 nm.

[0012] Unlike layer (A) of the layer package used in the present invention, layer (B) exclusively contains a metal effect pigment as a flake-type effect pigment. In the sense of the present invention, metallic effect pigments are considered to mean flake-like effect pigments made of metal or having at least one metallic layer. Examples of such pigments include aluminum pigments, commonly used in metallic finishes, which are in the form of so-called cornflakes or silver dollar coins and are suitable for use in coatings according to the present invention. Other aluminum pigments produced by wet grinding are also suitable, but aluminum pigments produced by vacuum deposition are not. The above-mentioned aluminum pigments are frequently used in paints and coatings, particularly in automotive finishes. Pure aluminum flakes can be coated with organic and / or inorganic materials to modify or optimize the use or color properties of the pigment. Bronze or brass pigments are also suitable as metallic effect pigments, but aluminum pigments are preferred. Metallic effect pigments are commercially available from various manufacturers in a wide variety of types and sizes. A suitable particle size for metallic effect pigments is in the d50 range of 5 to 50 μm, preferably 10 to 35 μm. Since the particle size is reported by the manufacturer and can be selected accordingly, separate particle size measurement is not required. The size ratio of the metal effect pigment used in layer (B) of the coating according to the present invention is not particularly limited within the indicated range. That is, ordinary commercially available metal effect pigments can be used.

[0013] For example, suitable silver metallic effect pigments include aluminum pigments or pigment preparations such as Stapa® IL Hydrolan 2156, Stapa® IL Hydrolan 8154, and Stapa® IL Hydrolan 3580 from Eckart GmbH, Emeral® EMR-767E and Emeral® EMR-1227 from Toyal, or APE-5245-C33 or AQUA PASTE® 5500-C43 from Silverline. Examples of colored metallic effect pigments include Merck KGaA's Meoxal® series pigments, specifically Meoxal® F120-30 CWT Taklamakan Gold, Meoxal® F120-51 CWT Victoria Red, Meoxal® F120-58 CWT Wahiba Orange, and Meoxal® F121-51 CWT Atacama Red.

[0014] The metallic effect pigment is present in layer (B) of the coating layer package in an amount of 3 to 25% by mass, particularly 15 to 20% by mass, based on the mass of layer (B). The amount of metallic effect pigment used and the thickness of layer (B) are mutually equivalent. Layer (B) of the layered package may optionally contain finely powdered absorbent pigments or dyes in addition to metallic effect pigments, but will not contain further flake-like effect pigments. Examples of organic and inorganic coloring pigments and their size ratios are already described above. The thickness of layer (B) is limited to a range of 2 to ≤10 μm to prevent excessive attenuation of radar radiation due to the metallic effect pigment present in the layer. However, a slight attenuation of radar radiation is permissible to ensure the normal operation of the radar device in which the coating according to the present invention is located on the substrate in the beam path. As already mentioned above, the optimal thickness of layer (B) depends on the concentration of the metallic effect pigment in this layer (lower concentrations allow for the larger of the indicated thicknesses). Furthermore, the particle size of the metallic effect pigment used should be selected so that layer (B) as a separate layer does not appear opaque. The thickness of layer (B) is understood to mean the thickness of the solidified and dried layer, i.e., the dry layer thickness.

[0015] In the context of this invention, "radar-compatible" is understood to mean a coating having a dielectric constant of <30 when exposed to electromagnetic waves having a peak frequency of 76.5 GHz. Furthermore, the coating on the 350 μm PET substrate must have a one-way transmission attenuation of <2 dB when exposed to electromagnetic waves having a peak frequency of 76.5 GHz. The one-way transmission attenuation is preferably <1.5 dB. The dielectric constant of the coating and the unidirectional transmission attenuation of the coating on the substrate were measured using the RMS-D-77 / 79G instrument from perisens GmbH in Germany, in standard mode. The thickness of layer (A) of the layer system according to the present invention is set such that the total layer thickness of the layer package including layers (A) and (B) is in the range of 10 to 40 μm, preferably 15 to 25 μm.

[0016] The binders used in layers (A) and (B) of the layered package can be any conventional binders and binder systems that appear transparent in the solidified state. Here, all common types of binders used in conventional coating methods and compatible with the pigments used can be used. Solvent-based binder systems, aqueous binder systems, and radiation-curing binder systems can be used equally, insofar as certain factors that are common in the art of pigment selection and the art of coating methods are observed. Both layer (A) and layer (B) of the coating according to the present invention may contain further additives commonly used in the art, such as fillers, inhibitors, flame retardants, lubricants, rheological aids, dispersants, redispersants, defoamers, flow regulators, film-forming agents, adhesion promoters, drying promoters, photoinitiators, and the like. Depending on the binder system used, the coating composition used in the manufacture of layers (A) and (B) of the layered package may optionally include an organic solvent and / or water, but these are not present in the coating according to the present invention after the solidification of the two layers. Conventional solvent systems in the art can be used without restriction. Compositions corresponding to the binder systems, including solvents and additives, are well known to those skilled in the art and, in some cases, are commercially available as finished products in an uncolored state. The corresponding selection can be made by those skilled in the art based on the respective coloring and desired coating method to be used. The substrates to which the layer package according to the present invention, including layers (A) and (B), may be applied are plastic plates or films. Plastics commonly used in automotive construction can be used, and several examples include polycarbonate (PC), polypropylene (PP), polyurethane (PUR), polymethyl methacrylate (PMMA), acrylonitrile-butadiene-styrene (ABS), or acrylonitrile-ethylene-styrene (AES) substrates. These types of plastic plates or films have a certain fundamental attenuation of radar signals, which is only slightly increased by the coating located thereon. With respect to the radar performance of the coating according to the present invention, the value of the fundamental attenuation of radar signals for unidirectional transmission (present in each substrate) is included in the measurement. The fundamental attenuation of unidirectional transmission of radar signals caused solely by the substrate is shown in a separate example. Measuring the attenuation of radar signals caused solely by the coating is not possible for technical, equipment-related, or manufacturing-related reasons. Needless to say, the base material can be molded in three dimensions depending on its application. That is, it can have a three-dimensional external shape. Therefore, for example, a plastic plate intended to form a vehicle tailgate component will naturally have a different three-dimensional external shape than a plastic plate intended for a bumper. Generally, the three-dimensional shape of the base material is manufactured by conventional molding methods before applying the coating according to the present invention.

[0017] An essential core element of the coating according to the present invention on a substrate is a layer package comprising the above-described layers (A) and (B) directly arranged toward each other, wherein, depending on the embodiment, either layer (A) or layer (B) represents the outermost layer of the layer package as seen from the substrate. In addition, further layers (which may also be components of the coating according to the present invention) may optionally be positioned between the substrate and the first layer (layer (A) or layer (B) depending on the embodiment) and / or above the second layer (layer (A) or layer (B) depending on the embodiment). These types of additional layers are frequently used in automotive construction for one of the following purposes: to improve adhesion of the paint layer to the substrate, to provide a colored accent, and / or to improve the mechanical and chemical strength and weather resistance of the paint layer. These are primer layers, further colored layers, or outermost clear coats, the clear coats of which are generally designed to be colorless and transparent. The coatings according to the present invention may, advantageously, have a primer layer and / or a clear coat. According to the present invention, all conventional materials widely used in industry and therefore requiring no further explanation can be used herein.

[0018] The coating according to the present invention on a substrate can be advantageously used without adversely affecting the function of the radar device in all cases where a cover having a metallic finish appearance is to be provided on the radar device. This naturally applies particularly to cover components used in vehicle construction. The coating according to the present invention is preferably a vehicle finish. Due to its excellent optical properties, the coating according to the present invention can also be used for all kinds of finishes that visually correspond to conventional metallic finishes, and consumes only small amounts of the metallic effect pigments that are normally used. The presence of radar beam permeability may also play a secondary role, and the corresponding application fields are not limited to vehicle construction.

[0019] The present invention also relates to a method for manufacturing a radar-compatible coating containing a metallic effect pigment on a substrate, wherein a layer package comprising layers (A) and (B) is applied to an optionally pre-coated substrate including a plastic plate or a plastic film, where layer (A) contains at least one pigment having absorption properties and does not contain a metallic effect pigment, layer (B) contains a flake-like effect pigment, the flake-like effect pigment is exclusively a metallic effect pigment, and layer (B) has a dry layer thickness in the range of 2 to ≤ 10 μm. Layers (A) and (B) of the layer package are arranged on the substrate in the order of (A)-(B) or (B)-(A). The full details of the materials relating to the composition of suitable plastic substrates and layers (A) and (B) have already been described above. Within this scope, the above description is referred to here. The two layers of the layered package can be applied to the substrate by conventional coating methods, such as spray coating, brush coating, in-mold coating, roller coating, coil coating, and curtain coating. This type of coating method is common in large-scale industry and can be used skillfully without requiring specific adaptations. Only the thickness of layer (B) is set during application, resulting in a final dry layer thickness in the range of 2 to ≤10 μm. This is considerably smaller than the dry layer thickness of conventional metallic finishes containing equivalent metal effect pigments. However, those skilled in the art will be able to set such a dry layer thickness without difficulty based on their expertise. The plastic substrates used have predetermined radar properties and can optionally be pre-coated with, for example, one or more primer layers and / or coloring layers. However, if the coating as a whole needs to have radar-compatible properties, it must be ensured that any optionally additional layers present on each substrate do not contain metallic effect pigments or other components that could adversely affect the radar transparency required for the coating as a whole. Pre-coating a primer layer onto a plastic substrate is advantageous because, in particular, it improves the overall mechanical stability of the coating and enhances the adhesion of the first layer of the layered package to the substrate. In addition, the outermost clear coat is generally designed to be colorless and transparent to visible light, which is particularly advantageous for the mechanical stability and weather resistance of the coating. The clear coat is also preferably applied to the upper layer of the layered package in this invention as the outermost layer of the entire coating.

[0020] The present invention also relates to the use of the above-mentioned coating, which contains a metallic effect pigment, as a radar-compatible vehicle finish for vehicle parts. The coating can be applied to all vehicle parts based on plastic substrates. Metal substrates are unsuitable because they cannot guarantee the desired radar performance. The coating can be applied to external body parts intended as outer covers or shielding parts for radar devices installed in the interior of a vehicle, or it can be applied to the entire surface of suitable body parts. Examples of body parts include bumpers, tailgates, radiator grilles, wings, or parts thereof. The coating according to the present invention can, of course, be applied to other vehicle parts if only a metallic finish is of interest and radar performance is of secondary importance. In the latter case, the field of application of the present invention is also not limited to vehicle construction. The present invention will be described below with reference to examples, but the present invention is not limited thereto.

[0021] Examples The substrate used in each case was a 350 μm thick PET film (Hostaphan RN 350, Mitsubishi Polyester Film GmbH, Germany). * To measure the values ​​and color separation ΔE, Leneta's black / white panels were coated in the same manner as PET film. The coating was performed as an air-powered spray coating. The binder used was WBC 000, a preparation from MIPA SE (Germany).

[0022] Example 1 (see reference): As a reference for the target appearance of the coating, a coating composition colored solely with aluminum pigment is applied to the film as a single layer. [Table 1] PMC: Pigment mass concentration Al: Aluminum pigment (Stapa® IL Hydrolan 2156, Stapa® IL Hydrolan 8154, 1:1 mixture, Eckart) DLT: Dry layer thickness L * :L * a * b * Lightness value L at a specific measurement angle in the color space * Flop index: This is an indicator of brightness flop when the observation angle changes, and can be calculated using the following formula.

number

[0023] Examples 2-4 (Invention): [Table 2]

[0024] In each case, four coating operations are performed. The first three coating operations are carried out using a coating composition colored only with 18% by mass of Iriodin® 9602 Silver Grey SW (a silver-gray interference pigment with a silvery-white absorption color, containing iron oxide, Merck KGaA, Darmstadt). Since there is no intermediate drying, the three coating operations result in layer (A) of the layer package according to the present invention (triple application technique is required). As layer (B), a coating composition colored solely with 12% by mass (Ex.2), 15% by mass (Ex.3), or 18% by mass (Ex.4) of an aluminum pigment mixture (as described above) is applied. The table shows the dry layer thickness of the coating as a whole, including layers (A) and (B). Approximately the same amount of coating composition is applied in each case during each coating operation. The chromaticity of the sample is measured using a BYKMac i colorimeter (Byk-Gardner) in SMC5 mode. L on a black background in layer (A) * The 15 values ​​are performed using only organic or inorganic absorbing pigments in a completely opaque coating in four regions on a standardized black / white coated substrate. When a flake-like effect pigment with absorbing properties is used in layer (A), the chromaticity measurement of layer (A), particularly L against a black background, is performed. * The measurement of the 15 values ​​is performed by coating the substrate with a pigment having a mass concentration of 18% by mass. The concentration of the pigments used and the thickness of the coating layers are shown in each example of the individual layers and layer packages of the coating according to the present invention. The black / white panels used as the base material here conform to the ASTM E 1347 standard and are sold by Leneta under the name Metopac T12G panel. The table shows that increasing the concentration of aluminum pigment in the second layer (approximately 4-5 μm thick in each case) leads to an increase in the flop index and a decrease in the ΔE value, and the appearance of a conventional silver metallic finish according to the reference example can be simulated well to very well in Examples 2-4.

[0025] Radar wave transmission properties: The table below shows the dielectric constant (dielectric constant) of each layer structure and the attenuation of the radar signal (dB) for one beam pass (76.5 GHz). [Table 3]

[0026] Examples of the present invention demonstrate a clear reduction in radar radiation attenuation for a single beam pass compared to conventional metallic finishes using a reference sample. All coatings according to the present invention are far more suitable than conventional opaque metallic finishes containing aluminum pigments as radar-compatible coatings for vehicle components located within the beam path of radar systems, depending on technical requirements, while simultaneously offering excellent opacity and very good brightness flop.

[0027] Examples 5-7: Using the PET substrate and coating method described in Example 1, a completely opaque coating of RAL shade 7030 (stone gray, Example 5), 7033 (cement gray, Example 6), and 7035 (light gray, Example 7) is applied to the substrate as layer (A) in each example. A layer (B) colored with 15% by mass of flake aluminum pigment (Stapa® IL Hydrolan 2156, Stapa® IL Hydrolan 8154, 1:1 mixture, Eckart) is applied to layer (A) in each example. Individual results regarding the color characteristics or radar performance of each coating can be seen in Tables 3 and 4. [Table 4] [Table 5]

[0028] The above examples demonstrate that a metallic appearance can be achieved with high concealment and sufficient flop index. The coatings in Examples 5 and 6 exhibit unidirectional attenuation of radar signals within the target range, while in Example 7, it extends slightly beyond the target range.

[0029] Example 8: As described above, a coating (B) colored with 18% by mass of aluminum pigment is applied to a PET substrate according to Example 1 by spray application as described in Example 1. A coating colored with 18% by mass of Colorstream® F10-51 Lava Red (Merck KGaA, iron oxide on SiO2 substrate) is applied as layer (A) in three coating operations. Individual results regarding the color characteristics or radar performance of each coating can be seen in Tables 5 and 6. [Table 6] [Table 7]

[0030] Example 8 demonstrates that a coating with good light / dark flop and significantly lower unidirectional attenuation of radar signals than a standard commercially available metallic coating using only aluminum pigment can be obtained even with the layer structure (B)-(A) on the substrate. The coating according to the present invention exhibits visually attractive red metallic characteristics and good opacity.

Claims

1. A coating for a radar device cover component comprising a metallic effect pigment on a substrate, wherein the coating is - A layer (A) containing at least one pigment having absorption properties and not containing a metallic effect pigment, - A layer (B) containing a flake-like effect pigment, wherein the flake-like effect pigment is only a metal effect pigment other than an aluminum pigment manufactured by vacuum deposition, and layer (B) has a layer thickness in the range of 2 to 10 μm, It has at least one layer package consisting of, Layer (A) contains the pigment having absorption properties at a concentration in the range of 10 to 25% by mass based on the mass of layer (A), and layer (B) contains the metal effect pigment at a concentration in the range of 3 to 25% by mass based on the mass of layer (B). coating.

2. The coating according to claim 1, characterized in that the first layer comprises an organic absorbing pigment, an inorganic absorbing pigment, and / or a flake-like effect pigment having absorbing properties.

3. The coating according to claim 1 or 2, characterized in that the layer package, including layers (A) and (B), has a total layer thickness in the range of 10 to 40 μm.

4. The coating according to any one of claims 1 to 3, characterized in that layer (A) contains an interference pigment having a silvery-white absorption color as a flake-like effect pigment.

5. The coating according to any one of claims 1 to 3, characterized in that layer (A) contains an interference pigment having a red absorption color as a flake-like effect pigment.

6. The coating according to any one of claims 1 to 5, characterized in that the metal effect pigment in layer (B) is an aluminum pigment.

7. The coating according to any one of claims 1 to 6, characterized in that layer (B) contains the metal effect pigment at a concentration in the range of 15 to 20% by mass based on the mass of layer (B).

8. The coating according to any one of claims 1 to 7, characterized in that the substrate is a plastic plate or film, and the plate or film may have a three-dimensional outer shape.

9. The coating according to any one of claims 1 to 8, characterized in that a further layer may be located between the substrate and the layer package including layers (A) and (B), and / or on the layer package.

10. The coating according to claim 9, characterized in that the further one or more layers are a primer layer and / or an outermost clear coat.

11. The coating according to any one of claims 1 to 10, characterized in that it is a vehicle finish.

12. A method for manufacturing a coating according to any one of claims 1 to 11, - A layer (A) containing at least one pigment having absorption properties and not containing a metallic effect pigment is applied to a pre-coated substrate including a plastic plate or plastic film, and thereafter - A layer (B) containing a flake-like effect pigment, wherein the flake-like effect pigment is solely a metallic effect pigment, and layer (B) has a dry layer thickness in the range of 2 to 10 μm, and layer (B) is applied to layer (A). or - A layer (B) containing a flake-like effect pigment, wherein the flake-like effect pigment is solely a metallic effect pigment, and layer (B) has a dry layer thickness in the range of 2 to 10 μm, and layer (B) is applied to a pre-coated substrate including a plastic plate or plastic film, and thereafter - A layer (A) containing at least one pigment having absorption properties and not containing a metal effect pigment is applied to layer (B). A method characterized by the following.

13. The method according to claim 12, characterized in that layers (A) and (B) are applied by spraying, brushing, roller coating, coil coating, curtain coating, or in-mold methods.

14. The method according to claim 12 or 13, characterized in that the substrate is pre-coated with a primer layer.

15. The method according to any one of claims 12 to 14, characterized in that a clear coat is applied as the outermost layer of the coating to layer (B) of layer package (A)(B) or layer (A) of layer package (B)(A).

16. A vehicle part containing a substrate including a plastic plate or plastic film having at least one coating according to any one of claims 1 to 11.

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