Radar compatible plastic parts

Abstract

The present invention relates to a radar-compatible plastic part having a surface to which a coloured coating is applied which is free of metallic effect pigments, to a process for manufacturing radar-compatible plastic parts of this type and to their use, particularly in vehicle construction.

Description

[Technical field]

[0001] The present invention relates to a radar-compatible plastic part having a surface to which a coloured coating is applied which is free of metallic effect pigments, to a manufacturing process for a radar-compatible plastic part of this type and to its use, in particular in vehicle construction. [Background technology]

[0002] With the increasing number of automobiles capable of autonomous driving, radar devices that allow both distance measurement to other vehicles or traffic obstacles and measurement of the speed of other traffic participants require integration into corresponding automobile parts on a scale never before imagined. Such radar devices are typically mounted behind the bumpers of automobiles so as not to spoil the appearance of the automobile.

[0003] For many years, metallic paints, preferably silver metallic paints, have been one of the most popular automotive paints, especially for the private car sector. However, these metallic paints pose a major challenge for the optical design of the cover parts of radar devices installed inside such vehicles, because normal metallic paints containing aluminum-based effect pigments can reflect, attenuate or absorb radar waves, usually in the 76-81 GHz frequency band, to such an extent that the use of conventional metallic vehicle paints for the cover parts of radar devices in vehicles leads to an undesirable reduction in the functioning of the radar devices.

[0004] Therefore, there have been many attempts to provide a solution for covering a vehicle radar device that does not spoil the appearance of the vehicle and allows the installed radar device to fully perform its function.

[0005] For example, radiator grilles or corresponding cover parts designed as company logos and having substantially radar transparent areas and metal posts often have a layer of evaporated metal, such as indium, such that such components typically have a chrome-like appearance.

[0006] However, this type of coating is not suitable for vehicle parts that are located in the beam path of a radar device but are intended to leave the observer with the visual impression of a conventional silver metallic paint. The difficulty here is to achieve the strong lightness flop (a clear change from light to dark with a change in illumination or viewing angle) that is usual for metallic paints containing metallic pigments, and to achieve the greatest possible hiding power of this type of metallic paint, reducing the attenuation of the radar waves to a sufficient extent that the transmission of the radar waves allows a fully functional operation of the installed radar device.

[0007] JP 2004-244516 discloses a glossy product with high transparency to electromagnetic radiation, which can be used as a radiator grille, but also as a component of other vehicle parts, for example as a tailgate. Here, the layer on the polycarbonate panel can contain metal particles, such as zinc, tin, indium, etc., but can also be pigmented, instead, with interference pigments, for example titanium dioxide-coated mica. The particles are applied to the panel in a concentration of 3 to 8% by weight in a polyurethane-containing layer. A black-based coating is applied as a back coating.

[0008] The glossy product, which includes multiple layers, is described as having high transparency to electromagnetic waves and high gloss.

[0009] Good radar transparency can be achieved with interference pigments containing titanium dioxide coated mica in such coatings, but the hiding power of metallic finishes containing metallic pigments and the strong metallic brightness flop achievable with metallic pigments are hardly attained by this type of colorless transparent mica-based interference pigments alone with simple structure.

[0010] JP 2006-282886 A also discloses a radar-transparent coating for vehicle parts, which comprises an interference pigment layer on a plastic substrate, and omits metallic effect pigments. It is stated that the interference pigment is based on particularly smooth substrate particles, in order to allow the color change of the coating. Substrate flakes of silicon dioxide or aluminum oxide are proposed as suitable substrate flakes. However, the visual impression of a metallic finish cannot be realized with a layer that comprises this type of interference pigment on the plastic substrate to be coated as well. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] JP 2004-244516 A [Patent Document 2] Patent Publication No. 2006-282886 Summary of the Invention [Problem to be solved by the invention]

[0012] The object of the present invention is to provide a radar-compatible coated plastic part, in particular suitable for use as a cover part for a radar device in vehicle construction, which dispenses with conventional metal effect pigments, in particular aluminum pigments, in its pigmented coating and which is preferably as visually indistinguishable as possible from conventional silver-pigmented metallic finishes, in particular having the appearance, high hiding power and strong brightness flop of a silver-pigmented metal, while at the same time having good radar wave transparency.

[0013] It is a further object of the present invention to provide a manufacturing process for the above radar compatible coated plastic parts.

[0014] Moreover, a further object of the present invention is to demonstrate the use of this type of coated plastic parts. [Means for solving the problem]

[0015] The object of the present invention is achieved by a radar-compatible coated plastic part, which has an optionally precoated and / or pretreated surface to which a colored coating is applied that contains flake-shaped effect pigments without metallic effect pigments and that have absorbing properties, the colored coating being composed of a number of layers arranged one above the other, the flake-shaped effect pigments being present in each layer, at least two of the layers having mutually different geometrical layer thicknesses, and the surface of the plastic part being free of any further coloring or metal coating.

[0016] Furthermore, the object of the invention is achieved by a manufacturing process for coated radar-compatible plastic parts of this type, in which a colored coating comprising flake-shaped effect pigments having absorbing properties without metallic effect pigments is applied to the optionally precoated and / or pretreated surface of the plastic part, the colored coating being applied in a number of layers arranged one above the other, in which the flake-shaped effect pigments having absorbing properties are present in each layer, in which at least two of the layers have a geometrical layer thickness different from one another, and in which a drying step is carried out after the application of each layer, in which the surface of the plastic part is not provided with any further colored or metallic coating.

[0017] The object of the invention is also achieved by the use of a plastic part coated as described above as a radar compatible vehicle part. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The inventors have surprisingly found that it is possible to provide a cover part of a radar device of a vehicle structure with a colored coating comprising flake-shaped effect pigments, the colored coating as a whole being able to have visually silver-colored metallic properties without metallic effect pigments.

[0019] Flake effect pigments without any metallic layer generally do not cause strong attenuation of the radar signal in the coating, but they usually show no or almost no intrinsic absorption and only low hiding power. These properties have the consequence that opaque silver coatings with high gloss and strong brightness flop, as are characteristic of metallic finishes, cannot be achieved with conventional flake effect pigments, which are usually interference pigments, in standard coating processes for automobiles.

[0020] The aim was therefore to find conditions under which a colour coating could be obtained on a cover part for a radar device of a vehicle product which met the requirements of hiding power, brightness flop and radar compatibility as far as possible, without the presence of metallic effect pigments in the colour coating, but in which the visual appearance of a metallic finish could be imitated to an appropriate extent by the colour coating on the respective plastic part.

[0021] The present inventors have now discovered a coated plastic part having a colored coating which satisfies the above requirements.

[0022] According to the invention, the colored coating on the surface of the plastic part is composed of several layers arranged one above the other, which are preferably arranged one above the other over the entire surface in each case to cover the surface of the plastic part. The surface of the plastic part can be optionally precoated and / or pretreated. These are preferably precoatings, as is common in vehicle constructions, with a primer layer and / or a filler layer, or alternatively or additionally also electrostatic pretreatments on the respective surface. This type of precoat and / or pretreatment affects the adhesion, quality and durability of the subsequent colored coating, but does not affect the visually perceptible coloration.

[0023] In the color coating of the surface of the radar-compatible plastic part according to the invention, each of the individual layers contains flake-shaped effect pigments with absorbing properties, but no metallic effect pigments. At least two layers of the color coating have different geometric layer thicknesses from each other. Furthermore, the surface of the plastic part does not comprise any further color coating apart from the above-mentioned multi-layer color coating, nor does it comprise a metal coating, the latter not as a vapor-deposited metal layer, nor as a binder-containing coating with metallic effect pigments or other metallic pigments.

[0024] According to the invention, the color coating of the radar-compatible plastic part has a multi-layer structure, preferably having 2 to 4 layers arranged one above the other, where it is advantageous if the color coating has a first layer, which is located directly on the optionally precoated and / or pretreated surface of the plastic part and has a geometric layer thickness that is greater than the geometric layer thickness of a respective further layer of the color coating arranged on this first layer.

[0025] This first layer particularly preferably has a geometric layer thickness that is greater than the sum of the geometric layer thicknesses of all further layers of the pigmented coating. Likewise, it is particularly preferred if all layers other than the first layer each have the same geometric layer thickness.

[0026] The flake-shaped effect pigments having absorption properties in the colored coating on the surface of the plastic part according to the invention are preferably flake-shaped effect pigments having a silvery-grey absorption color.

[0027] The optical effect of flake interference pigments is generally composed of a combination of light reflection and transmission phenomena in a series of thin layers, on which this type of effect pigment is generally composed, usually on a flake support material. Here, only materials that are colorless and transmit visible light to the maximum extent are very often used, such as, for example, flake mica pigments coated with titanium dioxide. Such pigments may have silvery or colored interference colors, but are generally transparent and have no mass tone.

[0028] Interference pigments (such pigments are referred to below as flake pigments with absorbing properties) achieve their absorbing properties, and therefore their masstones, when the flake support or alternatively at least one of the layers located on the flake support is composed of a material with an inherent color, i.e. an absorbing color. These can be colored metal oxides, metal suboxides, metal oxynitrides, mixed metal oxides, oxygen-deficient metal oxides, or metal oxide hydrates. Also, interference pigments achieve their absorbing properties due to a layer containing an organic color pigment.

[0029] According to the invention, flake-shaped effect pigments having at least one layer which comprises or is composed of iron oxide (Fe(II) and / or Fe(III)), mixed oxides comprising iron oxide and titanium oxide, titanium suboxide or titanium oxynitride, or which have a layer which is composed of or contains carbon, are preferably used in the pigmented coating. One or more other layers which comprise colorless and transparent materials can furthermore be located on the flake-shaped support.

[0030] The iron oxides or iron oxide hydrates considered are Fe2O3, FeO, Fe3O4 or FeOOH. The mixed oxides of iron oxide and titanium oxide are often ilmenite (FeTiO3) or pseudobrookite (Fe2TiO5). Suitable titanium suboxides are TiO, Ti2O3, Ti3O5, Ti4O7, Ti2O, Ti3O or Ti6O.

[0031] The layer thicknesses of the absorbing layers comprising iron oxide, mixed oxides comprising iron oxide and titanium oxide, titanium oxynitride or titanium suboxide, or layers comprising or consisting of carbon, are set such that the effect pigment has a silvery-grey absorption colour. In contrast, all other layers optionally present on the support material do not contribute to the absorption colour.

[0032] Suitable further colourless and transparent layers on the flake-shaped support material are in particular layers comprising colourless metal oxides or metal oxide hydrates, such as tin oxide, titanium dioxide, zirconium oxide, silicon dioxide, silicon oxide hydrate, aluminium oxide or aluminium oxide hydrate.

[0033] Flake-like support materials that come into consideration are natural or synthetic mica, kaolin, talc or sericite, and also glass, calcium borosilicate, SiO2, TiO2 or Al2O3. The flaky supports used are preferably natural or synthetic mica or Al2O3 flakes.

[0034] Flake-like effect pigments of the above type are commercially available. They can be obtained, for example, from Merck KGaA under the trade names Iriodin® 9602 Silver-Grey SW, Iriodin® 9605 Blue Shade Silver SW or Iriodin® 9612 Silver-Grey Fine Satin SW. They are based on mica flakes and have at least one layer containing iron oxide or titanium suboxide.

[0035] It is also possible to use flake-shaped effect pigments with absorbing properties, which preferably have on a transparent support flake one or more interference layers, as a final layer a very thin light-transmitting layer made of carbon. Such pigments are described, for example, in EP-A-3795645 by the applicant.

[0036] It has been found that effect pigments with a silvery-grey absorption color are suitable for use as flake effect pigments with absorption properties in a colored coating, since the colored coating is intended to have a silvery metallic appearance. Due to the pigment structure in the form of a series of thin layers on the flake substrate, this type of effect pigment exhibits a visually perceptible luster when struck by incident light. The silvery-grey absorption color results in a sufficiently high brightness in the case of direct incidence of light.

[0037] These flake-form effect pigments having absorbent properties generally have a particle size in the range from 1 to 100 μm, in particular from 2 to 70 μm, particularly preferably from 3 to 20 μm. The thickness of the effect pigments is in the range from 0.1 to 2 μm.

[0038] The particle size of flake effect pigments can be determined by laser diffraction. The particle size and particle size distribution by volume are preferably determined using Malvern Instruments (Malvern Mastersizer 3000, APA300, product of Malvern Instruments Ltd., UK) in standard mode. However, typical particle size ratios can also be found in manufacturer data on publicly accessible product information sheets.

[0039] In this size range, if the amount of effect pigments with absorbing properties and the total layer thickness of the pigmented coating are set according to the invention, a sufficiently good hiding power of the pigmented coating can be obtained.

[0040] It is also advantageous to use absorbent flake-form effect pigments in mixtures in which the effect pigments used have different particle sizes.

[0041] According to the invention, the minimum amount of flake-like effect pigments with absorbing properties in the individual layers of the pigmented coating is 5% by weight, based on the weight of each of the (solid) individual layers. The maximum amount of flake-like effect pigments with absorbing properties in the individual layers of the pigmented coating is 40% by weight, based on the weight of the respective layer. These effect pigments are preferably used in a concentration of 10 to 30% by weight in each layer of the pigmented coating, based on the respective weight (dry weight) of the layer.

[0042] In particular, it is preferred that the content and type of absorbing flake-form effect pigments are the same in the individual layers of the pigmented coating, since this significantly simplifies the manufacturing process of the plastic bodies coated according to the invention and makes it possible to prevent undesirable color shifts in the coating as a whole.

[0043] In a first embodiment of the invention, no further flake-shaped effect pigments apart from the flake-shaped effect pigments having absorbing properties are present in the pigmented coating.

[0044] In a second embodiment of the invention, the flake-shaped effect pigments with absorbing properties are present in the pigmented coating in a mixture with flake-shaped effect pigments without absorbing properties, in which case the ratio of absorbing to non-absorbing flake-shaped effect pigments is in the range of 2:1 to 10:1. Mixtures of this type are preferably present in separate layers of a multi-layer pigmented coating, the mixing ratio being the same in each layer, in particular the same flake-shaped effect pigments being used in each layer.

[0045] Suitable non-absorbing flake-form effect pigments are in particular interference pigments having a silvery-grey interference color.

[0046] They are based on natural or synthetic mica, kaolin, talc or sericite or on transparent, colorless flaky support materials such as glass, calcium aluminum borosilicate, SiO2, TiO2 or Al2O3. The flaky support materials used are preferably natural or synthetic mica or Al2O3 flakes.

[0047] The flake-shaped support material is coated with one or more layers of colorless, transparent metal oxides or metal oxide hydrates, such as tin oxide, titanium dioxide, zirconium oxide, silicon dioxide, silicon oxide hydrate, aluminum oxide, aluminum oxide hydrate, etc. This type of flake-shaped effect pigment has simply an interference color and no masstones.

[0048] Commercially available interference pigments offered by various manufacturers are suitable. Preferably, an interference pigment with a silver-gray interference color is used. Here, as an example, Iriodin® 9103 Rutile Sterling Silver SW from Merck KGaA can be mentioned.

[0049] The non-absorbing flake effect pigments have a particle size in the range from 1 to 250 μm, in particular from 2 to 100 μm. The thickness of these effect pigments is in the range from 0.1 to 2 μm.

[0050] If a mixture of flake-shaped effect pigments is used in the pigmented coating according to the second embodiment of the invention, the minimum proportion of flaky effect pigments with absorbing properties in each layer of the pigmented coating is, as already mentioned above, 5% by weight, based on the weight of the respective layer. The proportion of absorbing flake-shaped effect pigments in each layer is preferably at least 10% by weight, and the total proportion of absorbing and non-absorbing flake-shaped effect pigments is in each case 40% by weight, based on the weight of the respective layer, observing the above-mentioned mixing ratio.

[0051] As already mentioned above, the same flake-form effect pigments, in each case the same weight and mixture ratios, are preferably used in each layer of the pigmented coating.

[0052] According to the invention, the total geometric layer thickness of the pigmented coating is in the range from 8 to 25 μm, preferably in the range from 10 to 20 μm.

[0053] Where convenient, the pigmented coating may be measured using optical measurements of the coating, such as hiding power (ΔE * ), brightness (L * 15), and may also contain one or more so-called absorbing pigments, provided that this does not adversely affect the lightness flop (flop index).

[0054] Suitable absorption pigments are organic or inorganic pigments with absorption properties. These are essentially standard organic or inorganic absorption pigments. All absorption pigments that are usually used in various industrial coatings can be used for this purpose. They are preferably available with particle sizes ranging from 10 to 500 nm, in particular from 10 to <100 nm. Preparations of absorption pigments are generally commercially available. Depending on the compatibility with the coating system used, for example Heucotint® W (Heubach, DE), Heucotint® UN (Heubach, DE), MIPA WBC (Mipa, DE), Standoblue® (Standox GmbH, DE), Standohyd® (Standox GmbH, DE), Vocaflex® (Arichemie, DE), Vocaplast® (Arichemie, DE), etc. come into consideration.

[0055] Suitable absorption pigments are, for example, isoindolidones, benzimideazoles, quinacridones, Cu phthalocyanines, perylenes, carbon black and / or dioxytitanium. Colored absorption pigments can be used in suitable mixtures to obtain neutral achromatic colors.

[0056] White, gray and black are not usually called colors in the specialist world, because they are achromatic optical phenomena that simply indicate the amount of light absorbed by the respective surface. However, in the present invention, in contrast, white, gray and black are intended to be called colors. In this respect, the coating on the surface of the plastic part according to the present invention can also be called "coloration", but the "coloration" that is preferably aimed at here is a visual silver metallic impression that can be expressed as "silver gray", and therefore represents a mixture of white and black when ignoring the gloss element.

[0057] The overall optical effect of the multilayer pigmented coating according to the invention on the surface of a plastic part produces a homogeneous silver metallic overall impression of the coating according to the invention with high hiding power, high gloss and a pronounced luminosity flop on application.

[0058] The hiding power here is L * ,a * ,b * ΔE can be determined by spectrophotometric measurement of the coated substrate in color space * It is determined from the value of the quantity ΔE * is the L against a standardized black and white background with an illumination angle of 45° and a viewing angle of 75°. * a * b * It is defined as the color separation of a sample in color space and is determined according to the following formula: ΔE * =√(ΔL *2 +Δa *2 +Δb *2 )

[0059] The lower the resulting numerical value of the color separation, the better the coating hides the background. Complete hiding of the background is generally not achievable with non-metallic effect pigments, but can be achieved substantially in the case of the present invention. The colored coatings used according to the present invention are applied to a black / white background in a layer thickness in the range of 14±2 μm and, measured under the above-mentioned measuring conditions, have a ΔE in the range of 0 to 3, preferably in the range of 0 to 1. * These values ​​indicate very good hiding power of the pigmented coating for the purposes of the present invention.

[0060] The scale used in the professional world for the lightness of a coating is the L * 15 value, which is the L * ,a * ,b * In color space, it is determined photometrically at an illumination angle of 45° and a viewing angle of 15°. To be suitable as a coating according to the invention, it must have a minimum lightness that is obtained both on a white underlayer and on a black underlayer.

[0061] Using the above mentioned effect pigments with a silver-grey absorption colour in a coloured coating, which is applied over the entire area of ​​a black / white background with a layer thickness of 14±2 μm and has an illumination angle of L * ,a * ,b * A lightness L of at least 80 on both a coated white background and on a coated black background when measured with a spectrophotometer in the color space * A colored coating having a color of 15 is obtained.

[0062] In addition, good lightness flop can also be achieved. As a standard, this is expressed as the flop index and is determined spectrophotometrically at an illumination angle of 45° and non-specular separations of 15°, 45° and 110° from the specular angle. Thus, according to the invention, the flop index on a black coated background is determined when a colored coating is applied in a layer thickness of 14±2 μm over the entire area of ​​a black / white background and at an illumination angle of 45° and viewing angles of 45° (at 15°), 45° (at 45°) and 45° (at 110°) the flop index on a black coated background is determined as follows: * ,a * ,b * When measured with a spectrophotometer in color space, it is at least around 12.

[0063] Typically in the art, the flop index is considered as a measure of brightness flop at various viewing angles and is determined according to the following formula: TIFF2024514973000001.tif2377

[0064] The upper limit is the lightness L * Neither the case of 15 nor the case of the Flop Index is appropriate, since both quantities have an open upper limit and measurements that exceed the stated minimum in each case have a positive effect on the overall optical result when observing hiding powers within the stated ranges.

[0065] Details regarding the spectrophotometric measurement method and instrumentation are provided in the Examples section.

[0066] Surprisingly, it has been found that the multi-layer color coating on the plastic substrate according to the present invention shows significantly better properties in terms of brightness or also in terms of brightness flop, as indicated by the flop index, compared with a single-layer coating of the same total layer thickness (dry layer thickness).This broadens the suitability of the plastic parts coated according to the present invention for use as cover parts of radar devices in automobiles.The color coating of the plastic parts according to the present invention is visually very similar to standard metal coatings.At the same time, the avoidance of effect pigments that are made of metal or contain a metal layer ensures good radar wave transparency, so that the radar device installed inside the vehicle is not visible and its function is not unacceptably impaired.

[0067] The pigmented coating on the plastic part according to the invention consists of two or more layers, preferably three or four layers, arranged one above the other, where the total dry layer thickness of the pigmented coating is in the range of 8 to 25 μm.

[0068] The dry layer thickness of the first layer of the colored coating located directly on the surface of the plastic part according to the invention is preferably at least 5 μm, more preferably 8 μm or more, representing a layer of the colored coating having a maximum dry layer thickness (the surface of the plastic part can optionally be precoated and / or pretreated as described above, the pretreatment and / or precoating not determining the perceptible color impression).

[0069] All further layers of the pigmented coating preferably have a smaller dry layer thickness than the first layer, with at least one of the layers, preferably two or three of the layers, having a dry layer thickness of <5 μm in each case. In particular, the dry layer thickness of at least one of the further layers is ≦4 μm or ≦3 μm, particularly preferably about 2 μm. These extremely small layer thicknesses can be present in particular in two or three of the further layers, and are particularly preferred when all layers except the first layer have the same small dry layer thickness.

[0070] In order to be able to combine such thin multi-layer structures to provide a visually attractive colored coating on the plastic part, smooth surfaces of the individual layers are necessary. These result from interfaces between the individual layers of the colored coating, which are arranged substantially parallel to the surface of the plastic part. The interfaces are obtained by intermediate drying after application of the individual layers of the colored coating. Due to the intermediate drying, the absorbing flake-shaped effect pigments in the individual layers and, in the second embodiment, the non-absorbing flake-shaped effect pigments in the individual layers are aligned with their main axes approximately parallel to the surface of the plastic part or to the precoat on the surface of the plastic part, so that a good reflection of the incident light is achieved in the individual layers of the colored coating.

[0071] The pigment loading of the individual layers here is likewise at least 5% by weight of flake-form effect pigments having absorbing properties and in each case a maximum of 40% by weight of flake-form effect pigments in total, based on the weight of the individual layers. Preferably, 10 to 30% by weight of flake-form effect pigments having absorbing properties are used in each layer of the pigmented coating.

[0072] "Radar compatible" in the sense of the present invention means a coating that has a dielectric constant of <30 when exposed to electromagnetic waves with a peak frequency of 76.5 GHz. Furthermore, a coating on a 350 μm PET substrate should have a one-way transmission attenuation of less than 2 dB when exposed to electromagnetic waves with a peak frequency of 76.5 GHz.

[0073] Measurements of the dielectric constant of the coating and the one-way transmission attenuation of the coating on the substrate are carried out using a perisens GmbH (Germany) RMS-D-77 / 79G instrument in standard mode.

[0074] The binders used for the pigmented coating are conventional binders and binder systems that appear transparent in the set state. Here, one can rely on all standard binder types that are used in conventional coating processes and that are compatible with the pigments used. Solvent-based binder systems, water-based binder systems, radiation-curable binder systems can be used as well, as long as the specific factors customary in the art regarding the choice of pigment and the coating process are observed.

[0075] The pigmented coating may contain further additives which are conventional in the art, such as, for example, fillers, inhibitors, flame retardants, lubricants, rheological aids, dispersants, redispersants, defoamers, flow control agents, film formers, adhesion promoters, drying accelerators, photoinitiators, and the like.

[0076] In the case of the second desired dry layer, if present, in the case of each further layer of the pigmented coating in the range of less than 5 μm, the use of rheological assistants is generally indicated.The rheological assistants considered are, for example, substances such as BaSO4, polyamide powders, silicates or other rheological assistants well known to those skilled in the art, but in particular cellulose-based nanofibers.The latter are particularly preferably used.These rheological assistants in each case allow the formation of a consistent, particularly thin, pigment-containing layer on the surface to be coated.

[0077] Depending on the binder system used, the coating composition used to produce the colored coating optionally also contains organic solvents and / or water, which are no longer present in the colored coating of the plastic parts according to the invention after solidification or drying of the individual layers. Solvent systems that are customary in the art can be used without restriction.

[0078] The corresponding compositions of the binder systems, including solvents and additives, are well known to those skilled in the art and are sometimes even commercially available as finished products in unpigmented form. A corresponding selection can be made by the skilled artisan on the basis of the respective pigment to be used and the desired coating process.

[0079] Plastic plates or films come into consideration when the coating is intended to be radar compatible, such as plastic parts to which a multi-layer colored coating is applied. Plastics that are usually used in automotive construction can be used here, such as substrates of polycarbonate (PC), polypropylene (PP), polyurethane (PUR), polymethylmethacrylate (PMMA), acrylonitrile-butadiene-styrene (ABS), acrylonitrile-ethylene-styrene (AES), to name only a few. Plastic plates or films of this type have a certain basic attenuation of the radar signal, which has to undergo only a small increase due to the colored coating located thereon. With regard to the radar compatibility of the plastic parts according to the invention, the value of the basic attenuation for the one-way transmission of the radar signal that exists due to the respective plastic substrate is included in the measurement value. The basic attenuation of the one-way transmission of the radar signal caused only by the plastic substrate is shown separately in Example 4. Measurement of the radar signal attenuation caused only by the coating is not possible for technical installation-related reasons.

[0080] If the colored coating is intended to be applied to any substrate for purely optical reasons and if the concern is not the radar compatibility of the coating, it is of course possible to use metallic or metal-containing substrates as well.

[0081] It goes without saying that the plastic part can be three-dimensionally shaped, i.e. have a three-dimensional profile, depending on the application. Thus, for example, a plastic sheet intended to form a component of an automobile tailgate will naturally have a different three-dimensional profile than a plastic sheet intended as a bumper. In general, the three-dimensional shape of the plastic part is produced by a conventional molding process before the application of the colored coating.

[0082] An essential core element of the plastic part according to the invention is the above-mentioned multi-layer pigmented coating. In addition, further layers, which may also be part of the plastic part according to the invention, can optionally be located between the plastic surface of the plastic part and the first layer of the pigmented coating and / or above the pigmented coating.

[0083] One or more layers that may be optionally located between the plastic surface of the plastic part and the colored coating are, as already mentioned above, primer layers or filler layers. Such additional layers are often used in automotive constructions to optionally improve the adhesion of the paint layer to the respective substrate and / or to improve the mechanical and chemical strength of the paint layer. These are primer layers, which do not determine the visually perceptible color of the coated plastic part. In contrast, the outermost layer is preferably applied to the surface of the colored coating also to improve the weather resistance of the colored coating. This type of layer is usually called a clear coat and is generally designed to be transparent and colorless, but can also contain very small amounts of pigments. The plastic product according to the invention can also advantageously have a primer layer and / or a clear coat. According to the invention, all conventional materials that are widely used in industry and therefore do not require further explanation can be used.

[0084] The plastic parts coated according to the invention can be advantageously used in all cases, where the radar device is provided with a cover, which has a visually silver effect finish, without the functionality of the radar device being adversely affected. This of course applies in particular to cover parts used in vehicle construction. The plastic parts coated according to the invention are preferably vehicle parts. Thanks to their good optical properties, such colored coatings can of course also be used for all types of finishes that are intended to visually correspond as far as possible to conventional silver metallic finishes. Also, the radar wave transparency present can play a subordinate role here, and the corresponding area of ​​use is not limited to automobile manufacturing.

[0085] The invention also relates to a process for the production of radar-compatible plastic parts, in which a pigmented coating which is free of metallic effect pigments and which comprises flake-shaped effect pigments having absorbing properties is applied to an optionally precoated and / or pretreated surface of the plastic part, the pigmented coating being applied in a number of layers arranged one above the other, the flake-shaped effect pigments having absorbing properties being present in each layer, at least two of the layers having geometrical layer thicknesses which differ from one another, and drying being performed after the application of each layer, and the surface of the plastic product being free of further pigmentation or metallic coating.

[0086] All material details concerning the material composition of suitable plastic parts and multi-layer pigmented coatings have already been described above and, to that extent, are hereby incorporated by reference.

[0087] Application of the individual layers of the pigmented coating to the surface of the optionally pretreated plastic part can be carried out by conventional coating processes, such as spray processes, in-mold processes, roller coating processes, curtain coating processes, or electrostatic application processes.

[0088] This type of coating process is standard in large scale industry and can be used according to the art.

[0089] Preferably, a spray process or an electrostatic application process is used.

[0090] Conventional spraying techniques, which allow obtaining dry layer thicknesses of 5 to 25 μm in a single spraying operation, are suitable for producing the first layer of the pigmented coating. This application step is completed by intermediate drying.

[0091] However, for the application of the second layer of the pigmented coating and, if present, each further layer, with a dry layer thickness of <5 μm, a spraying process is particularly suitable, which allows the layers arranged one above the other to be applied successively in several work steps to the first layer of the pigmented coating, with very small dry layer thicknesses of the individual layers. These preferably 1 to 3 layers are in each case likewise dried after the application of each individual layer, so that an interface is formed between each individual layer (part-layers). The drying temperature of the individual layers depends on the respective binder system and the solvent used and is at least 20° C. Temperatures up to a maximum of 150° C., preferably up to a maximum of 100° C., can be used.

[0092] The amount of flake-like effect pigments with absorbing properties in the colored coating here is at least 5% by weight, based on the dry layer weight, for each individual layer, but can be in the range of 10 to 40% by weight, in particular in the range of 10 to 30% by weight. The dry layer thickness of at least one of the layers is <5 μm, preferably ≦4 μm, in particular ≦3 μm or about 2 μm. Preferably, two or three layers have such a small layer thickness.

[0093] High pigment concentrations in the respective layers of the pigmented coating in the case of very small dry layer thicknesses of the individual layers can be established by very drastically reducing the proportion of binder in the respective coating composition (solids content of about 6 to 7% by weight) and drastically increasing the proportion of solvent (preferably water). In order that very dilute coating compositions of this type can form a continuous coating film on the surface to be coated, various auxiliaries, in particular rheological auxiliaries, are added, which ensure that a suitable viscosity of the coating composition is established, so that it can be applied to the background by a spraying process and exhibit good flow properties. In the course of the subsequent drying process, small solid masses with a very high proportion of flake-like effect pigments remain on the respective background as a single layer, in which the effect pigments are present, the main axes of which are well aligned essentially parallel to the respective coated surface.

[0094] As a rheological aid, the cellulosic nanofibers are preferably added in an amount of 5 to 20 wt. %, based on the weight of the respective coating composition.

[0095] Due to the multiple application of individual layers arranged one above the other and the intermediate drying of each of these layers, the flake-like effect pigments in the multi-layer pigmented coating can be particularly well oriented, which results in a high reflection of the incident light at the surface of the pigmented coating. This in particular increases the lightness flop of the pigmented coating, and allows high hiding power and good overall lightness of the coating to be achieved at the same time. Thus, coated plastic parts whose pigmented coatings visually correspond substantially to silver metallic coatings, but have good radar compatibility, can be obtained by using flake-like effect pigments with absorbing properties in the pigmented coating, without using any type of metallic pigment in the coating as a whole.

[0096] The pigmented coating is preferably applied in a total dry layer thickness ranging from 8 to 25 m.

[0097] In detail, the application of the pigmented coating is carried out in 2 to 4 steps by applying 2 to 4 layers successively, in each case one above the other, in a spray process, the amount of flake-shaped effect pigments with absorbing properties in each layer being at least 5% by weight, based on the dry weight of the respective layer, and the drying process being carried out at a temperature of at least 20° C. after the application of each layer.

[0098] The surface of the plastic parts used with the preset radar properties can optionally be electrostatically pretreated and / or precoated, for example with one or more primer or filler layers as already mentioned above. In order to ensure the radar compatibility of the coating as a whole, however, it must be ensured that none of the layers optionally additionally present on the surface of the plastic parts contains metal effect pigments, other metal pigments, metal layers or other components which may impair the essential radar transparency of the coating as a whole.

[0099] The surface precoat of the plastic part with a primer layer is advantageous, because such a precoat layer improves, among other things, the mechanical stability of the overall coating and the adhesion of the first layer of the layer package to the substrate. In addition, the outermost clear coat, which is designed to be largely colorless and transparent to visible light, is particularly advantageous for the mechanical stability and weather resistance of the coating. Also in the present invention, the outermost clear coat is preferably applied to the surface of the colored coating as the outermost layer of the overall coating. Also, clear coats containing absorption pigments or effect pigments with a PMC of less than 2% are sometimes used in technical applications. According to the present invention, such clear coats do not imply coloring and can be used on the surface of the plastic part according to the present invention as well.

[0100] It goes without saying that the coating as a whole is subjected to at least one curing step, which is carried out after application and drying of the pigmented coating and / or after application of the clear coat. The curing of coatings on substrates, including plastic substrates, in particular in the automotive field, is a standard process in the art and does not need to be described in more detail.

[0101] The invention also relates to the use of the above-mentioned plastic parts coated with a colored coating free of metal effect pigments as vehicle parts, in particular as radar-compatible vehicle parts. It can be used, for example, as an external body part intended as an outer cover or shielding part for a radar device installed inside the vehicle. Body parts that may be mentioned are, in particular, bumpers, tailgates, radiator grilles, wings or parts thereof. Of course, the colored coating can also be applied to vehicle parts other than those mentioned, and to metal-containing substrates, in particular when only the visual appearance of the metallic finish is of interest and radar compatibility is not necessary. In the latter case, the application area of ​​the invention is likewise not limited to vehicle structures.

[0102] The present invention will now be described with reference to examples, but is not limited thereto. EXAMPLES

[0103] To measure the optical properties of the colored coatings, they are applied to standardized black / white coated Leneta panels (white and black standard coatings are present in the respective component areas). The coating is carried out as a pneumatic spray coating. The binder used is the formulation WBC000 from MIPA SE (Germany). Finally, all samples are coated with a standard two-component clear coat.

[0104] Various mixtures of flake-form effect pigments are used in the pigmented coating.

[0105] Effect pigment 1: Effect pigment with absorbing properties based on mica, the coating contains SnO2, TiO2, iron oxide and auxiliaries, particle size <15 μm, silver-grey absorbing color.

[0106] Effect pigment 2: Effect pigment without absorption properties based on mica, coating contains SnO2, TiO2 and auxiliaries, particle size <100 μm, silver-grey interference color.

[0107] The mixing ratio of the coating composition is as follows: Composition A: Pigment 1: Pigment 2 = approx. 3:1 Composition A': pigment 1:pigment 2=approximately 3:1 Composition B: Pigment 1: Pigment 2 = approx. 8:1 Composition B': Pigment 1: Pigment 2 = approximately 8:1

[0108] Each composition further contains a standard absorbing pigment (present at 0.55% in PMC). EXAMPLES

[0109] To determine the hiding power of the pigmented coatings, coating compositions A, A', B and B' with a pigment mass concentration of 28% by weight in each case, based on the weight of the solid coating, are applied to standardized black-and-white coated panels, both in a single coating operation (comparison) and in a multicoat application according to the invention, drying for 5 minutes at 80° C. after each application step. In the case of the multicoat application according to the invention, the pigmented coating is applied in 4 layers (28% by weight PMC in each case, layer thicknesses 9, 2, 2, 2 μm, drying for 5 minutes at 80° C. in each case). Lower color separation ΔE * The closer to 75° appears, the better the hiding power of each color coating.

[0110] Table 1: Hiding power TIFF2024514973000002.tif34155 Layers: number of layers of color coating, 1st layer: Comparison 4th layer: the present invention PMC: Mass concentration of color pigment in each layer DLT: Dry layer thickness of the entire pigmented coating L * : L at viewing angle 15° and lighting angle 45° * a * b * Lightness value in color space L * ΔE * : L over a standardized black and white background (illumination angle 45°, viewing angle 75°) calculated according to the following formula: * a * b * Color separation of the sample in color space ΔE * =√(ΔL *2 +Δa *2 +Δb *2 )

[0111] Flop index: A measure of lightness flop at various viewing angles (illumination angle 45°, viewing angles 45° (at 15°), 45° (at 45°), 45° (at 110°)) calculated according to the following formula: TIFF2024514973000003.tif2377 EXAMPLES

[0112] To determine the lightness of each coating, coating compositions A, A', B and B' are applied to each black background as in Example 1. In addition to the pneumatic spray application process, an electrostatic process is used because it is the standard process used in OEM coating equipment. The greater the lightness value L * 15, it is possible to visually mimic a coating that is simply opaquely pigmented with aluminum pigments. Table 2: Brightness TIFF2024514973000004.tif56155

[0113] In the case of the coloured layer structures according to the invention, high lightness values ​​that exceed those in the case of a single application of the corresponding coating composition can be obtained with each coating process and each effect pigment mixture used. EXAMPLES

[0114] All coatings produced in Example 2 are remeasured to determine the flop index. Table 3: Flop Index TIFF2024514973000005.tif56155

[0115] Conventional silver metal coatings, typically containing aluminum pigments, have a flop index in the range of about 12 to 17. This range can be achieved on all substrates coated with a pigmented coating according to the present invention.

[0116] Colorimetric measurements of the samples are carried out using a model BYKMac i colorimeter (Byk-Gardner) in SMC5 mode.

[0117] The black / white panels used here as substrates comply with the ASTM E 1347 standard and are sold by Leneta under the name Metopac T12G panels.

[0118] From these tables it can be seen that the pigmented coatings with each of the mixtures used herein, which contain flake-shaped effect pigments with a silver-grey absorption color and flake-shaped effect pigments with a silver-grey interference color, and each of the coating process variants used, achieve very high hiding power at the same time as good brightness and good brightness flop, and are therefore able to visually imitate in a good or very good manner metallic coatings containing aluminum pigments.Since no metallic pigments are present in the coating, no significant attenuation of radar waves is expected by the corresponding coatings on plastic substrates. EXAMPLES

[0119] To determine the radar transmittance, a PET film (Hostaphan RN 350, Mitsubishi Polyester Film GmbH, Germany) with a thickness of 350 μm is used as substrate in each case. The coating is carried out as a pneumatic spray coating. The binder used is WBC 000 from MIPA SE.

[0120] The pigmented coating applied in each case was a layer containing the effect pigment mixture shown in Table 4 having a silver-grey absorption color or a silver-grey interference color in one or four layers in each case and dried as described in Example 1.

[0121] Table 4 shows the dielectric constant (dielectric constant) of each layer structure and the attenuation (dB) of the radar signal for a single beam passage (76.5 GHz) (instrument: RMS-D-77 / 79G manufactured by perisens GmbH (Germany), standard mode).

[0122] The uncoated PET substrate has a dielectric constant of about 3.0 and a radar attenuation of 1.05 dB.

[0123] For comparison, a coating comprising a monolayer on a PET substrate containing a commercial aluminum pigment, with 18 wt. % PMC and a DLT of about 22 μm, has a dielectric constant of about 74.9 and a one-way attenuation of the radar signal of about 4.5 dB under the same measurement conditions. Table 4: Radar wave penetration rate TIFF2024514973000006.tif39155

[0124] The multi-stage coating process does not adversely change the radar transparency of a pigmented coating on a plastic part (here a plastic film) that is merely pigmented with metal-free effect pigments. Thus, the plastic part according to the invention has good radar transparency.

Claims

1. A radar-compatible coated plastic part, said plastic part having an optionally precoated and / or pretreated surface to which a pigmented coating is applied, said coating comprising flake-shaped effect pigments having absorbing properties, without metallic effect pigments, 1. A radar-compatible coated plastic part, wherein the pigmented coating is composed of a number of layers arranged one above the other, wherein the flake-shaped effect pigments having absorbing properties are present in each of the layers, at least two of the layers having different geometric layer thicknesses from one another, and wherein the surface of the plastic part does not have any further pigmentation or metallization.

2. 10. The radar compatible plastic part of claim 1, wherein the color coating has two to four layers arranged one above the other.

3. 2. The radar compatible plastic part of claim 1, wherein the colored coating comprises a first layer, the first layer being located directly on the optionally precoated and / or pretreated surface of the plastic part and having a geometric layer thickness greater than a geometric layer thickness of each of the further layers disposed on the first layer.

4. 2. The radar compatible plastic part of claim 1, wherein the flaked effect pigment having absorbing properties is present in each of the layers of the pigmented coating in an amount of at least 5% by weight, based on the weight of each of the layers of the pigmented coating.

5. 2. The radar-compatible plastic part according to claim 1, wherein apart from the flake-shaped effect pigment having absorbing properties, no further flake-shaped effect pigments are present in the pigmented coating.

6. 2. The radar compatible plastic part of claim 1, wherein the absorbing flake effect pigments are present in the pigmented coating in a mixture with non-absorbing flake effect pigments.

7. The coloured coating was applied over the entire area of ​​a black / white background with a total layer thickness of 14±2 μm and was measured at an illumination angle of 45° and a viewing angle of 75°. * , a * , b * A color separation ΔE between the coated white background and the coated black background, ranging from 0 to 3, as measured by a spectrophotometer in color space. * 2. The radar compatible plastic part of claim 1, having a

8. The coloured coating was applied over the entire area of ​​a black / white background with a total layer thickness of 14±2 μm and was measured under an illumination angle of 45° and a viewing angle of 15°. * , a * , b * A lightness L of at least 80 on both the painted white background and the painted black background as measured by a spectrophotometer in color space. * 15. The radar compatible plastic part of claim 1 .

9. The coloured coating was applied over the entire area of ​​a black / white background with a total layer thickness of 14±2 μm and was measured at an illumination angle of 45° and at viewing angles of 45° (at 15°), 45° (at 45°) and 45° (at 110°). * , a * , b * 2. The radar-compatible plastic part of claim 1, having a flop index of at least 12 on the painted black background in each case, as measured with a spectrophotometer in color space.

10. 2. The radar compatible plastic part of claim 1, wherein the colored coating comprises, as a flake effect pigment having absorbing properties, an effect pigment having a silver-grey absorbing color.

11. 11. The radar-compatible plastic part according to claim 10, wherein the effect pigment with a silvery-grey absorption colour is a pigment having on a transparent flake-shaped support at least one layer comprising iron oxide, titanium suboxide, titanium oxynitride or a mixture of iron oxide and titanium oxide, or having a layer comprising or consisting of carbon.

12. 2. The radar compatible plastic part of claim 1, wherein said color coating comprises flake effect pigment in each of said layers of said color coating at a concentration ranging from 5 to 40 weight percent, based on said weight of each of said layers of said color coating.

13. 10. The radar compatible plastic part of claim 1, wherein the colored coating has a total layer thickness in the range of 8 to 25 μm.

14. 10. The radar compatible plastic part of claim 1, wherein the plastic part is a plastic plate or film, and the plastic part can optionally have a three-dimensional profile.

15. 10. The radar compatible plastic part of claim 1, wherein at least one further layer is located above the colored coating.

16. 16. The radar compatible plastic part of claim 15, wherein the further layer is an outermost clear coat.

17. 10. The radar compatible plastic part of claim 1, wherein the surface of the plastic part is pre-coated with a primer layer and / or a filler layer and / or is electrostatically pre-treated.

18. 2. A manufacturing process for radar-compatible plastic parts according to claim 1, in which a coloured coating comprising flaky effect pigments with absorbing properties, without metallic effect pigments, is applied to an optionally pretreated and / or pre-treated surface of a plastic part, said coloured coating being applied in a number of layers arranged one above the other, said flaky effect pigments with absorbing properties being present in each of said layers, at least two of said layers having different geometric layer thicknesses from one another, drying being performed after the application of each of said layers, and said surface of the plastic part being free of any further colouring or metallisation.

19. 20. The process of claim 18, wherein the pigmented coating is applied with a total dry layer thickness in the range of 8 to 25 μm.

20. 20. The process of claim 18, wherein the color coating comprises, in each of the layers, flake effect pigments in an amount of from 5 to 40% by weight, based on the weight of each of the layers of the color coating.

21. 20. The process of claim 18, wherein the application of the pigmented coating is performed by a spraying process, a roller coating process, a curtain coating process, an in-mold process, or an electrostatic application process.

22. 22. The process according to claim 21, wherein the application of the pigmented coating is carried out as a spray process in two to four part steps by applying in each case two to four layers successively one above the other, the amount of flake-shaped effect pigments having absorbing properties in each of said layers being at least 5% by weight, based on the dry weight of each of said layers, and drying being carried out at a temperature of at least 20° C. after application of each of said layers.

23. 20. The process of claim 18, wherein at least one of the layers of the pigmented coating has a dry layer thickness of <5 μm.

24. 19. The process according to claim 18, wherein the surface of the plastic part is pre-coated with a primer layer and / or a filler layer and / or is electrostatically pre-treated.

25. 20. The process of claim 18, wherein a clear coat is applied as an outermost layer to the surface of the pigmented coating.

26. 20. The process of claim 18, wherein the plastic part is a plastic plate or film, and the plastic part can optionally have a three-dimensional profile.

27. 13. Use of the radar compatible plastic part according to claim 1 as a vehicle part.

28. A vehicle component comprising the radar compatible plastic part of claim 1.