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 radar-compatible plastic parts having a surface coated with a colored coating without metallic pigments, a manufacturing process for this type of radar-compatible plastic part, and, in particular, its use in vehicle structures. [Background technology]

[0002] As the number of autonomous vehicles increases, radar devices capable of both measuring the distance to other vehicles or obstacles and measuring the speed of other road users need to be integrated into corresponding automotive components on a scale previously unimaginable. Such radar devices are typically mounted behind the vehicle's bumper to avoid compromising the car's appearance.

[0003] For many years, metallic paints, preferably silver metallic paints, have been among the most popular automotive paints, particularly in the passenger car sector. However, these metallic paints present a significant challenge in the optical design of cover components for radar devices installed inside such vehicles, because conventional metallic paints containing aluminum-based effect pigments can reflect, attenuate, or absorb radar waves, typically in the 76-81 GHz frequency range, to such an extent that the conventional use of metallic automotive paints on cover components for radar devices inside vehicles results in an undesirable reduction in the functionality of the radar devices.

[0004] Therefore, there have been many attempts to provide solutions for covering vehicle radar devices that do not detract from the vehicle's appearance and allow the installed radar device to fully perform its function.

[0005] For example, a corresponding cover component, designed as a radiator grille or company logo and having a substantially radar-transmitting area and metal supports, often has a layer of vapor-deposited metal, such as indium. Such components typically have a chrome-like appearance.

[0006] However, this type of coating is unsuitable for vehicle parts located in the beam path of radar devices but intended to leave the observer with the visual impression of conventional silver metallic paint. The challenge here lies in achieving the strong brightness flop (a clear change from light to dark with changes in illumination or viewing angle) that is common in metallic paints containing metallic pigments, and reducing radar wave attenuation to a degree sufficient to achieve the greatest possible opacity of this type of metallic paint, allowing radar waves to penetrate and the installed radar device to function fully.

[0007] Japanese Patent Publication No. 2004-244516 discloses a glossy product having high transmittance to electromagnetic radiation, which can be used as a radiator grille, but also as a component of other vehicle parts, such as a tailgate. Here, the layer on the polycarbonate panel may contain metal particles such as zinc, tin, and indium, but can also 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 weight. A black-based coating is applied as a back coating.

[0008] It is stated that glossy products containing multiple layers have high transmittance to electromagnetic waves and high gloss.

[0009] Good radar wave transmission can be achieved in such coatings with interference pigments containing titanium dioxide-coated mica. However, the opacity of metallic finishes containing metallic pigments and the strong metallic brightness flop achievable with metallic pigments are hardly obtainable with interference pigments based on this type of colorless, transparent mica, which has a simple structure.

[0010] Further, Japanese Patent Application Laid-Open No. 2006-282886 discloses a radar wave transmissive coating for vehicle parts that includes an interference pigment layer on a plastic substrate and omits a metallic effect pigment. In order to enable color change of the coating, it is described that the interference pigment is particularly based on smooth substrate particles. Substrate flakes of silicon dioxide or aluminum oxide have been proposed as suitable substrate flakes. However, a visual impression of a metallic finish cannot be achieved with a layer containing this type of interference pigment on the plastic substrate to be coated, either.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0012] An object of the present invention is, in particular, suitable for use in cover parts of radar devices in a vehicle structure, omits conventional metallic effect pigments, particularly aluminum pigments, in its colored coating, and preferably has as little visual difference as possible from a conventional silver-colored metallic finish. In particular, it has the appearance of a silver-colored metal, high hiding power, and strong brightness flop, and at the same time has good radar wave transmissivity, and provides a radar-compatible coated plastic part.

[0013] A further object of the present invention is to provide a manufacturing process for the above-mentioned radar-compatible coated plastic part.

[0014] Furthermore, a further object of the present invention is to show the use of this type of coated plastic part.

Means for Solving the Problems

[0015] The object of the present invention is achieved by a radar-compatible coated plastic part, the plastic part having an optionally pre-coated and / or pre-treated surface to which a colored coating containing a flake-like effect pigment having absorption properties is applied without metallic effect pigments, the colored coating consists of multiple layers arranged vertically, the flake-like effect pigment is present in each layer, at least two of the layers have different geometric layer thicknesses, and the surface of the plastic part has no further coloring or metallic coating.

[0016] Furthermore, the object of the present invention is achieved by a manufacturing process for this type of coated radar-compatible plastic part, wherein a colored coating containing a flake-like effect pigment having absorption properties without metallic effect pigments is applied to an optionally pre-coated and / or pre-treated surface of the plastic part, the colored coating is applied in multiple layers arranged vertically, the flake-like effect pigment having absorption properties is present in each layer, at least two of the layers have different geometric layer thicknesses from each other, a drying process is performed after the application of each layer, and the surface of the plastic part is free from any further coloring or metallic coating.

[0017] Furthermore, the object of the present invention is achieved by using the above-described coated plastic part as a radar-compatible vehicle component. [Modes for carrying out the invention]

[0018] The inventors have found that, surprisingly, it is possible to provide a cover component for a radar device of a vehicle structure having a colored coating containing a flake-effect pigment, and that the colored coating as a whole can visually have silvery metallic properties without the metallic effect pigment.

[0019] Flake effect pigments without any metallic layer generally do not cause strong attenuation of radar signals within the coating; they typically exhibit little to no inherent absorption and only low opacity. These properties result in opaque silver coatings with high gloss and strong brightness flop, characteristic of metallic finishes, which cannot be achieved in standard automotive coating processes with conventional flake effect pigments, which are typically interference pigments.

[0020] Therefore, the objective was to find conditions under which a colored coating that satisfies the requirements of concealment, brightness flop, and radar compatibility as much as possible can be obtained on cover components for radar devices of vehicle products without the presence of metallic effect pigments within the colored coating, while the visual appearance of a metallic finish can be appropriately mimicked by the colored coating on each plastic component.

[0021] The inventors have found a coated plastic part having a colored coating that fully satisfies the above conditions.

[0022] According to the present invention, the colored coating on the surface of a plastic part consists of multiple layers arranged vertically, which are preferably arranged vertically across the entire surface in each case, covering the surface of the plastic part. The surface of the plastic part can optionally be pre-coated and / or pre-treated. These are preferably pre-coatings common in vehicle structures having a primer layer and / or filler layer, or alternative or additional electrostatic pre-treatments on each surface. This type of pre-coating and / or pre-treatment affects the adhesion, quality, and durability of the subsequent colored coating, but does not affect the visually perceptible coloring.

[0023] In the radar-compatible colored coating for the surface of a plastic part according to the present invention, each individual layer contains a flake-like effect pigment having absorption properties, but no metallic effect pigment. At least two of the layers of the colored coating have different geometric layer thicknesses. Furthermore, the surface of the plastic part does not have any further colored coating apart from the multilayer colored coating described above, nor does it have a metallic coating, the latter not as a vapor-deposited metal layer, nor as a binder-containing coating containing a metallic effect pigment or other metallic pigment.

[0024] According to the present invention, a colored coating for a radar-compatible plastic part has a multilayer structure and preferably has 2 to 4 layers, one of which is positioned on top of the other. Here, it is preferable that the colored coating has a first layer, the first layer is positioned directly on the optionally pre-coated and / or pre-treated surface of the plastic part and has a geometric thickness greater than the geometric thickness of any further individual layers of the colored coating positioned on this first layer.

[0025] This first layer is particularly preferably geometrically thicker than the sum of the geometric thicknesses of all further layers of the colored coating. Similarly, it is particularly preferable that each of all layers other than the first layer has the same geometric thickness.

[0026] The flake-like effect pigment having absorption properties within a colored coating on the surface of a plastic part according to the present invention is preferably a flake-like effect pigment having a silver-gray absorption color.

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

[0028] Interference pigments (hereinafter referred to as flake pigments with absorption properties) achieve absorption properties and thus master tone when at least one of the flake support or alternatively, a layer located on the flake support, is composed of a material having an inherent color, i.e., an absorption color. These can be colored metal oxides, metal suboxides, metal oxynitrides, mixed metal oxides, oxygen-deficient metal oxides, or metal oxide hydrates. Interference pigments also achieve absorption properties due to a layer containing an organic coloring pigment.

[0029] According to the present invention, flake-like effect pigments having a silver-gray absorption color, comprising or composed of at least one layer containing iron oxide (Fe(II) and / or Fe(III)), a mixed oxide comprising iron oxide and titanium oxide, titanium dioxide, or titanium oxynitride, or comprising or containing a layer of carbon, are preferably used within a colored coating. One or more other layers comprising a colorless transparent material may further be located on the flake-like support.

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

[0031] The thickness of the absorption layer containing iron oxide, a mixed oxide containing iron oxide and titanium oxide, titanium oxynitride, or titanium dioxide, or a layer containing or composed of carbon, is set so that the effect pigment has a silvery-gray absorption color. In contrast, all other layers optionally present on the support material do not contribute to the absorption color.

[0032] A suitable further colorless and transparent layer on the flake-like support material is, in detail, a layer containing a colorless metal oxide or metal oxide hydrate, such as tin oxide, titanium dioxide, zirconium oxide, silicon dioxide, silicon oxide hydrate, aluminum oxide, or aluminum oxide hydrate.

[0033] The flake-like support materials to be considered are natural or synthetic mica, kaolin, talc, or sericite, and also glass, calcium borosilicate, SiO2, TiO2, or Al2O3. The flake-like support used is preferably natural or synthetic mica or Al2O3 flakes.

[0034] The above-described type of flake-type effect pigments are commercially available. These can be obtained from Merck KGaA under trade names such as Iriodin® 9602 Silver-Grey SW, Iriodin® 9605 Blue Shade Silver SW, or Iriodin® 9612 Silver-Grey Fine Satin SW. These are based on mica flakes and have at least one layer containing iron oxide or titanium oxide.

[0035] Preferably, a flake-like effect pigment having absorption properties can be used, which has one or more interference layers on a transparent support flake, and a very thin light-transmitting layer composed of carbon as a final layer. Such a pigment is described, for example, in European Publication No. 3795645 by the present applicant.

[0036] Effect pigments with a silvery-gray absorbent color have been found suitable for use as flake-type effect pigments with absorbent properties within a colored coating, because 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 a flake-type substrate, this type of effect pigment exhibits a visually perceptible gloss when incident light strikes it. The silvery-gray absorbent color provides sufficiently high brightness in the case of direct light incidence.

[0037] These absorbent flake-type effect pigments generally have a particle size in the range of 1 to 100 μm, particularly 2 to 70 μm, and especially preferably 3 to 20 μm. The thickness of the effect pigment is in the range of 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 relative to volume are preferably determined using Malvern Instruments (Malvern Mastersizer 3000, APA300, a 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] Within this size range, if the amount of the effect pigment having absorption properties and the total thickness of the colored coating are set according to the present invention, a sufficiently good opacity of the colored coating can be obtained.

[0040] Furthermore, it is advantageous to use absorbent flake-type effect pigments in mixtures of effect pigments with different particle sizes.

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

[0042] In particular, it is preferable that the content and type of absorbent flake-like effect pigments are the same in each individual layer of the colored coating, because this significantly simplifies the manufacturing process of the plastic body coated according to the present invention and prevents undesirable color shifts in the overall coating.

[0043] In the first embodiment of the present invention, no further flake-effect pigments other than the flake-effect pigment having absorption properties are present within the colored coating.

[0044] In a second embodiment of the present invention, a flake-effect pigment having absorbing properties is present in a colored coating of a mixture with a flake-effect pigment without absorbing properties. In this case, the ratio of the absorbing flake-effect pigment to the non-absorbing flake-effect pigment is in the range of 2:1 to 10:1. This type of mixture is preferably present in individual layers of a multilayer colored coating, with the same mixing ratio in each layer, and in particular, the same flake-effect pigment is used in each layer.

[0045] A suitable flake-effect pigment with no absorbency is, in detail, an interference pigment having a silvery-gray interference color.

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

[0047] The flake-like 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 dioxide hydrate, aluminum oxide, or aluminum oxide hydrate. This type of flake-like effect pigment simply has interference colors and no master tone.

[0048] Commercially available interference pigments from various manufacturers are suitable. Preferably, interference pigments with a silver-gray interference color are used. Hereinafter, one example is Merck KGaA's Iriodin® 9103 Rutile Sterling Silver SW.

[0049] Non-absorbent flake-type effect pigments have particle sizes ranging from 1 to 250 μm, particularly from 2 to 100 μm. The thickness of these effect pigments ranges from 0.1 to 2 μm.

[0050] When a mixture of flake-like effect pigments is used in a colored coating according to a second embodiment of the present invention, the minimum proportion of flake-like effect pigments having absorbing properties in each layer of the colored coating is 5% by weight, based on the weight of each layer, as already described above. The proportion of absorbing flake-like effect pigments in each layer is preferably at least 10% by weight, and the total proportion of absorbing and non-absorbing flake-like effect pigments is 40% by weight in each case, based on the weight of each layer, in accordance with the mixing ratio described above.

[0051] As already mentioned above, in each case, the same flake-type effect pigment in the same weight and mixing ratio is preferably used for each layer of the colored coating.

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

[0053] If it is advantageous, the colored coating is used to measure the optical properties of the coating, e.g., the opacity (ΔE). * ), brightness (L * 15) and may also contain one or more so-called absorbing pigments, provided that they do not adversely affect the lightness flop (flop index).

[0054] Suitable absorbent pigments are organic or inorganic pigments with absorbent properties. These are essentially standard organic or inorganic absorbent pigments. All absorbent pigments commonly used in various industrial coatings can be used for this purpose. They are preferably available in particle sizes ranging from 10 to 500 nm, and especially from 10 to <100 nm. Preparations of absorbent pigments are generally commercially available. Depending on compatibility with the coating system used, examples include 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.

[0055] Suitable absorbent pigments include, for example, isoindolidones, benzimidoazoles, quinacridones, Cu phthalocyanines, perylenes, carbon black, and / or dioxytitanium. Colored absorbent pigments can be used in appropriate mixtures to obtain neutral achromatic colors.

[0056] White, gray, and black are not typically referred to as colors in the professional world, because they are achromatic optical phenomena that simply indicate the amount of light absorbed by their respective surfaces. However, in this invention, in contrast, white, gray, and black are intended to be called colors. To this extent, the coating on the surface of a plastic part according to this invention can also be called "coloring," where the "coloring" preferably intended is a visually silvery metallic impression that can be described as "silver-gray," and therefore represents a mixture of white and black when gloss is ignored.

[0057] The overall optical effect of the multilayer colored coating according to the invention on the surface of the plastic part results in an overall impression of a homogeneous silver metallic coating according to the invention with high hiding power, high gloss, and distinct lightness flop regarding the coating.

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

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

[0060] The scale used for the lightness of the coating in the expert world is the L * 15 value of the coating, which is optically determined at an illumination angle of 45° and a viewing angle of 15° in the L * , a * , b * color space of a standardized black / white background. For the coating to be suitable according to the present invention, this must have the minimum lightness obtained both on a white underlayer and on a black underlayer.

[0061] When the above-mentioned effect pigment, which has a silver-gray absorbent color, is used in the colored coating, it is applied to the entire area of ​​the black / white background with a layer thickness of 14±2 μm, and at the illumination angle L * ,a * ,b * When measured with a spectrophotometer in a color space, the lightness L is at least 80 on both a covered white background and a covered black background. * A colored coating having 15 is obtained.

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

[0063] Typically in this technical field, the flop index is considered a measure of brightness flop at various viewing angles and is determined according to the following formula. TIFF0007902200000001.tif2377

[0064] Bringing up the upper limit is like valuing brightness L * Neither the case of 15 nor the case of the flop exponent is appropriate, because both quantities have an open upper limit, and measurements exceeding the stated minimum in each case will have a positive effect on the overall optical results when observing the opacity within the stated range.

[0065] Details regarding the spectrophotometric measurement method and instruments are described in the Examples section.

[0066] Surprisingly, the multilayer colored coating on a plastic substrate according to the present invention has been found to exhibit significantly better properties in terms of brightness or brightness flop, as indicated by the flop index, compared to a single-layer coating of the same total layer thickness (dry layer thickness). This broadens the suitability of plastic parts coated according to the present invention for use as cover components for automotive radar devices. The colored coating of plastic parts according to the present invention is visually very similar to a standard metal coating. At the same time, by avoiding effect pigments composed of metal or containing a metal layer, good radar wave transmission is ensured, and as a result, radar devices installed inside a vehicle are not visible and their function is not impaired to an unacceptable degree.

[0067] The colored coating on a plastic part according to the present invention consists of two or more layers, preferably three or four layers, arranged vertically. The total dry layer thickness of the colored coating is in the range of 8 to 25 μm.

[0068] The dry layer thickness of the first colored coating directly located on the surface of the plastic part according to the present invention is preferably at least 5 μm, more preferably 8 μm or more, representing a colored coating layer having the maximum dry layer thickness (the surface of the plastic part may optionally be pre-coated and / or pre-treated as described above, and the pre-treatment and / or pre-coating does not determine the perceptible color impression).

[0069] All further layers of the colored coating preferably have a dry layer thickness smaller than the first layer, and at least one of the layers, preferably two or three of the layers, has 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, especially preferably about 2 μm. These extremely small layer thicknesses can be present 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] For such thin, multilayer structures to be combined to provide a visually appealing colored coating on a plastic part, smooth surfaces of the individual layers are required. These arise from the interfaces between the individual layers of the colored coating, which are positioned substantially parallel to the surface of the plastic part. The interfaces are obtained by intermediate drying after the application of the individual layers of the colored coating. For intermediate drying, the main axes of the absorbing flake effect pigments within the individual layers, and the non-absorbing flake effect pigments within the individual layers in the second embodiment, are aligned substantially parallel to the surface of the plastic part or the pre-coat on the surface of the plastic part, and thus good reflection of incident light is achieved in the individual layers of the colored coating.

[0071] The pigment filling in each individual layer here is similarly at least 5% by weight of a flake-effect pigment having absorbent properties, and in each case, based on the weight of the individual layer, the total is up to 40% by weight of the flake-effect pigment. Preferably, 10 to 30% by weight of the absorbent flake-effect pigment is used within each layer of the colored coating.

[0072] In the sense of this invention, "radar compatibility" means 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 a 350 μm PET substrate must have a unidirectional transmission attenuation of less than 2 dB when exposed to electromagnetic waves having a peak frequency of 76.5 GHz.

[0073] The dielectric constant of the coating and the unidirectional transmission attenuation of the coating on the substrate are measured using a Perisens GmbH (Germany) RMS-D-77 / 79G instrument in standard mode.

[0074] The binders used in colored coatings are conventional binders and binder systems that appear transparent when solidified. Here, we can rely on all standard binder types that are used in conventional coating processes and are compatible with the pigments used. Solvent-based binder systems, aqueous binder systems, and radiation-curable binder systems can be used insofar as the specific factors common in this art regarding pigment selection and coating processes are observed.

[0075] The colored coating may include further additives that are common in this art, such as fillers, inhibitors, flame retardants, lubricants, rheological additives, dispersants, redispersants, defoamers, flow regulators, film-forming agents, adhesion promoters, drying promoters, and photopolymerization initiators.

[0076] For the second desired dry layer, and for each further layer of the colored coating, if present, in the range of less than 5 μm, the use of rheological additives is generally indicated. Rheological additives considered include, for example, BaSO4, polyamide powders, silicates, or other rheological additives well known to those skilled in the art, but in particular, cellulose nanofibers. The latter are particularly preferred. These rheological additives enable the formation of a consistent and particularly thin pigment-containing layer on the coated surface in each case.

[0077] Depending on the binder system used, the coating composition used to manufacture the colored coating may optionally include organic solvents and / or water, but these are no longer present in the colored coating of the plastic part according to the present invention after the solidification or drying of individual layers. Any solvent system that is common in the art can be used without limitation.

[0078] Corresponding compositions of 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 pigments to be used and the desired coating process.

[0079] When the coating is intended to be radar-compatible, such as a plastic part to which a multi-layer colored coating is applied, a plastic sheet or film is considered. Plastics commonly used in automotive structures can be used here, to name just a few, including, for example, polycarbonate (PC), polypropylene (PP), polyurethane (PUR), polymethyl methacrylate (PMMA), acrylonitrile-butadiene-styrene (ABS), and acrylonitrile-ethylene-styrene (AES) substrates. This type of plastic sheet or film has a certain degree of fundamental attenuation of radar signals, which should only be slightly increased by the colored coating placed on it. Regarding the radar compatibility of plastic parts according to the present invention, the value of fundamental attenuation for unidirectional transmission of radar signals present due to each plastic substrate is included in the measurement. The fundamental attenuation for unidirectional transmission of radar signals caused solely by the plastic substrate is shown separately in Example 4. Measuring radar signal attenuation caused solely by the coating is impossible due to technical and equipment-related reasons.

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

[0081] It goes without saying that plastic parts can have a three-dimensional shape depending on their application, that is, they can have a three-dimensional external form. Therefore, for example, a plastic sheet intended to form a component of a car's tailgate will naturally have a different three-dimensional external form than a plastic sheet intended to be a bumper. Generally, the three-dimensional shape of a plastic part is generated by a conventional molding process before the application of a color coating.

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

[0083] One or more layers that can be optionally positioned between the plastic surface of a plastic part and the colored coating are, as already described above, primer layers or filler layers. Such additional layers are often optionally used in automotive structures to 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 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 may also contain a very small amount of pigment. Plastic products according to the present invention may also conveniently have a primer layer and / or a clear coat. According to the present invention, all conventional materials that are widely used industrially and therefore do not require further explanation can be used.

[0084] Plastic parts coated according to the present invention can be used in all cases, where a radar device is provided with a cover, and the cover has a visually silvery finish without adversely affecting the functionality of the radar device. This naturally applies in detail to cover parts used in vehicle structures. Plastic parts coated according to the present invention are preferably vehicle parts. Thanks to their good optical properties, such colored coatings can of course be used for all types of finishes intended to visually correspond as closely as possible to conventional silver metallic finishes. Radar wave transmission can also play a secondary role here, and the corresponding application area is not limited to automobile manufacturing.

[0085] Furthermore, the present invention relates to a process for manufacturing radar-compatible plastic parts, wherein a colored coating containing a flake-like effect pigment having absorption properties but without metallic effect pigments is applied to the optionally pre-coated and / or pre-treated surface of the plastic part, the colored coating is applied in multiple layers arranged vertically, the flake-like effect pigment having absorption properties is present in each layer, at least two of the layers have different geometric layer thicknesses, drying is performed after the application of each layer, and the surface of the plastic product does not have any further coloring or metallic coating.

[0086] All material details regarding the material composition of appropriate plastic parts and multi-layer colored coatings have already been described above. Within that scope, they are referenced here.

[0087] The application of individual layers of colored coating to the surface of a optionally pre-treated 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 coating processes.

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

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

[0090] Conventional spraying techniques that can achieve a dry layer thickness of 5 to 25 μm in a single spray operation are suitable for producing the first layer of a colored coating. This coating step is completed by intermediate drying.

[0091] However, for the application of the second layer of colored coating having a dry layer thickness of <5 μm, and each further layer if present, a spray process is particularly suitable, as the spray process allows for the continuous application of the layers positioned above and below the first layer of colored coating in multiple work steps, with each individual layer having a very small dry layer thickness. These preferably 1 to 3 layers are dried similarly after the application of each individual layer in each case, resulting in the formation of interfaces between each individual layer (part-layers). The drying temperature of the individual layers depends on the respective binder system and solvent used, and is at least 20°C. Temperatures up to 150°C, preferably up to 100°C, can be used.

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

[0093] High pigment concentration in each layer of a colored coating, in the case of very small dry layer thicknesses of individual layers, can be established by significantly reducing the proportion of binder in each coating composition (solids content is about 6 to 7% by weight) and significantly increasing the proportion of solvent (preferably water). Various auxiliaries, in particular rheological auxiliaries, are added so that this type of very dilute coating composition can form a continuous coating film on the surface to be coated. The rheological auxiliaries ensure that the appropriate viscosity of the coating composition is established, and as a result, it can be applied to the background by a spray process and exhibit good flow properties. During the subsequent drying process, small solid lumps with a very high proportion of flake-like effect pigment remain on each background as a single layer, within which the effect pigment is present, and the main axis of the effect pigment is well aligned, essentially parallel to each coated surface.

[0094] As a rheological additive, cellulose nanofibers are preferably added in an amount of 5 to 20% by weight, based on the weight of each coating composition.

[0095] Due to the multiple coating of individual layers arranged vertically and the intermediate drying of each of these layers, the flake-effect pigments within the multilayer colored coating can be particularly well oriented, resulting in high reflection of incident light on the surface of the colored coating. This improves the brightness flop of the colored coating, and simultaneously achieves high opacity and good overall brightness of the coating. Therefore, a coated plastic part that visually corresponds substantially to a silver metallic coating but has good radar compatibility can be obtained by using flake-effect pigments with absorption properties within the colored coating, without using all types of metallic pigments in the overall coating.

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

[0097] In detail, the application of the colored coating is carried out in 2 to 4 steps by spraying 2 to 4 layers sequentially, in each case applied from top to bottom, the amount of flake-like effect pigment with absorption properties in each layer is at least 5% by weight based on the dry weight of each layer, and the drying process is carried out at a temperature of at least 20°C after the application of each layer.

[0098] The surface of the plastic component to be used, having predetermined radar characteristics, may optionally be electrostatically pre-treated and / or pre-coated with one or more primer or filler layers, for example, as already described above. However, in order to ensure the radar compatibility of the overall coating, it is necessary to ensure that none of the optionally additional layers present on the surface of the plastic component contain metallic effect pigments, other metallic pigments, metallic layers, or other components that may impair the essential radar wave transmission of the overall coating.

[0099] Pre-coating the surface of plastic parts with a primer layer is advantageous because such a pre-coat layer improves, among other things, the overall mechanical stability of the coating and the adhesion of the first layer of the layer package to the substrate. In addition, an outermost clear coat, designed to be generally colorless and transparent to visible light, is particularly advantageous for the mechanical stability and weather resistance of the coating. In the present invention, the outermost clear coat is preferably applied to the surface of a colored coating as the outermost layer of the overall coating. Clear coats containing absorbing or effect pigments with less than 2% PMC are also occasionally used in technical applications. According to the present invention, such a clear coat does not imply coloring and can similarly be used on the surface of plastic parts in accordance with the present invention.

[0100] Needless to say, the overall coating undergoes at least one curing process, which is performed after the application and drying of the colored coating and / or after the application of the clear coat. In detail, curing of coatings on substrates, including plastic substrates, in the automotive sector is a standard process in this art and does not require further explanation.

[0101] Furthermore, the present invention relates to the use of the aforementioned plastic parts coated with a colored coating without metallic pigments as vehicle parts, and more specifically as radar-compatible vehicle parts. This can be used, for example, as an external body part intended as an outer cover or shielding part for radar devices installed inside a vehicle. Body parts that can be mentioned include, in particular, bumpers, tailgates, radiator grilles, wings, or their components. Of course, the colored coating can also be applied to vehicle parts other than those mentioned, and to metal-containing substrates, especially when only the visual appearance of a metallic finish is of interest and radar compatibility is not required. In the latter case, the scope of application of the present invention is similarly not limited to vehicle structures.

[0102] The present invention will be described below with reference to examples, but will not be limited thereto. [Examples]

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

[0104] Various mixtures of flake-type effect pigments are used for colored coatings.

[0105] Effect Pigment 1: An effect pigment with absorption properties based on mica; the coating contains SnO2, TiO2, iron oxide, and auxiliary agents; particle size <15 μm; silver-gray absorption color.

[0106] Effect Pigment 2: An effect pigment based on mica with no absorption properties; the coating contains SnO2, TiO2, and auxiliary agents, with a particle size <100 μm and a silver-gray interference color.

[0107] The mixing ratio of the coating composition is as follows: Composition A: Pigment 1: Pigment 2 = approximately 3:1 Composition A': Pigment 1:Pigment 2 = approximately 3:1 Composition B: Pigment 1: Pigment 2 = approximately 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 measure the opacity of the colored coatings, coating compositions A, A', B, and B', each having a pigment mass concentration of 28 wt% in each case based on the weight of the solid coating, were applied to standardized black and white coated panels in both a single coating operation (comparative) and a multi-coat application according to the present invention, and dried at 80°C for 5 minutes after each coating step. In the case of the multi-coat application according to the present invention, the colored coating was applied in four layers (28 wt% PMC in each case, layer thicknesses of 9, 2, 2, and 2 μm, dried at 80°C for 5 minutes in each case). Lower color separation ΔE * The closer the angle to 75°, the better the opacity of each colored coating.

[0110] Table 1: Concealing Power TIFF0007902200000002.tif34155 Layers: Number of colored coating layers, Layer 1: Comparison 4 layers: The present invention PMC: Mass concentration of coloring pigments in each layer DLT: Dry thickness of the entire colored coating L * : L at a viewing angle of 15° and illumination angle of 45° * a * b * Lightness value L in color space * 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 a sample in a color space ΔE * =√(ΔL *2 +Δa *2 +Δb *2 )

[0111] Flop index: A measure of brightness flop at various viewing angles (illumination angle 45°, viewing angle 45° (at 15°), 45° (at 45°), 45° (at 110°)) calculated according to the following formula. TIFF0007902200000003.tif2377 [Examples]

[0112] To determine the brightness of each coating, coating compositions A, A', B, and B' are applied to their respective black backgrounds, as in Example 1. In addition to the pneumatic spray coating process, an electrostatic process is used because the electrostatic coating process is standard practice in OEM coating facilities. Larger brightness values ​​L * The more 15 appears, the better visually it can mimic a coating simply opaquely colored with aluminum pigment. Table 2: Brightness TIFF0007902200000004.tif56155

[0113] In the case of the colored layer structure according to the present invention, a lightness value higher than that obtained in the case of a single application of the corresponding coating composition can be obtained in each coating process and in each of the effect pigment mixtures used. [Examples]

[0114] To measure the flop index, all coatings manufactured in Example 2 are remeasured. Table 3: Flop exponents TIFF0007902200000005.tif56155

[0115] Conventional silver metal coatings containing aluminum pigments generally have a flop index in the range of about 12 to 17. This range can be achieved on all substrates to which the colored coating according to the present invention is applied.

[0116] The colorimetric measurement of the sample will be performed using a Model BYKMac i colorimeter (Byk-Gardner) in SMC5 mode.

[0117] 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 panels.

[0118] These tables show that colored coatings having each of the mixtures used herein, including a flake-effect pigment having a silver-gray absorption color and a flake-effect pigment having a silver-gray interference color, and each of the variations of the coating process used, achieve very high opacity simultaneously with good brightness and good brightness flop, and thus can visually mimic metallic coatings containing aluminum pigments in a good or very good manner. Since metallic pigments are not present in the coating, no significant attenuation of radar waves by the corresponding coating on a plastic substrate is expected. [Examples]

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

[0120] The colored coating applied in each case is a layer containing the effect pigment mixture shown in Table 4, which has a silver-gray absorbent color or a silver-gray interference color in one or four layers in each case, and is dried as described in Example 1.

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

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

[0123] A coating containing a commercially available aluminum pigment, including a single layer on a PET substrate having 18 wt% PMC and approximately 22 μm DLT, exhibits a dielectric constant of approximately 74.9 and a unidirectional attenuation of the radar signal of approximately 4.5 dB under the same measurement conditions for comparison. Table 4: Radar wave transmittance TIFF0007902200000006.tif39155

[0124] The multi-stage coating process does not negatively alter the radar wave transmittance of the colored coating on the plastic part (in this case, the plastic film), which is simply colored with a metal-free effect pigment. Therefore, the plastic part according to the present invention has good radar wave transmittance.

Claims

1. A radar-compatible coated plastic cover component for a radar device, wherein the plastic cover component has a optionally pre-coated and / or pre-treated surface to which a colored coating comprising a flake-like effect pigment having light-absorbing properties is applied, without metallic effect pigments. The colored coating consists of multiple layers arranged vertically, the flake-like effect pigment having light-absorbing properties is present in each of the layers, at least two of the layers have different geometric layer thicknesses, and the surface of the plastic cover part does not have any further coloring or metallic coating. The aforementioned flake-like effect pigment is a radar-compatible coated plastic cover component having at least one layer on a transparent flake-like support containing iron oxide, titanium oxide, titanium oxynitride, or a mixture of iron oxide and titanium oxide, or a layer containing or composed of carbon.

2. The radar-compatible plastic cover component according to claim 1, wherein the colored coating has two to four layers arranged vertically.

3. The radar-compatible plastic cover part according to claim 1, wherein the colored coating has a first layer, the first layer is located directly on the optionally pre-coated and / or pre-treated surface of the plastic cover part and has a geometric thickness greater than the geometric thickness of any further individual layers disposed on the first layer.

4. The radar-compatible plastic cover component according to claim 1, wherein the flake-like effect pigment having the light-absorbing properties is present in each of the layers of the colored coating in an amount of at least 5% by weight, based on the weight of each of the layers of the colored coating.

5. The radar-compatible plastic cover component according to claim 1, wherein no further flake-like effect pigments, other than the aforementioned light-absorbing flake-like effect pigments, are present within the colored coating.

6. The aforementioned colored coating is applied to the entire area of ​​the black / white background with a total layer thickness of 14 ± 2 μm, and is visible at an illumination angle of 45° and a viewing angle of 75°. * , a * , b * When measured with a spectrophotometer in color space, the color separation ΔE between the coated white background and the coated black background ranges from 0 to 3. * A radar-compatible plastic cover component according to claim 1, having the following characteristics.

7. The aforementioned colored coating is applied to the entire area of ​​the black / white background with a total layer thickness of 14 ± 2 μm, and is illuminated at a 45° illumination angle and a 15° viewing angle. * , a * , b * When measured with a spectrophotometer in the color space, the lightness L is at least 80 on both the coated white background and the coated black background. * A radar-compatible plastic cover component according to claim 1, having 15.

8. The colored coating is applied over the entire area of the black / white background with a total layer thickness of 14 ± 2 μm and has an L value when measured with a spectrophotometer in the a, b color space at an illumination angle of 45° and viewing angles of 45° (at 15°), 45° (at 45°), and 45° (at 110°). * , a * , b * The plastic cover part conforming to radar according to claim 1, which has at least 12 flop indices on the applied black background in each case when measured with a spectrophotometer in the a, b color space.

9. The radar-compatible plastic cover part according to claim 1, wherein the colored coating includes a flake-shaped effect pigment having light-absorbing properties, and the effect pigment having a silver-gray absorption color.

10. The radar-compatible plastic cover part according to claim 1, wherein the colored coating comprises, in each of the layers of the colored coating, a flake-like effect pigment in a concentration ranging from 5 to 40% by weight, based on the weight of each of the layers of the colored coating.

11. The radar-compatible plastic cover component according to claim 1, wherein the colored coating has a total layer thickness in the range of 8 to 25 μm.

12. The radar-compatible plastic cover component according to claim 1, wherein the plastic cover component is a plastic plate or film, and the plastic cover component can optionally have a three-dimensional external shape.

13. The radar-compatible plastic cover component according to claim 1, wherein at least one further layer is located above the colored coating.

14. The radar-compatible plastic cover component according to claim 13, wherein the further layer is an outermost clear coat.

15. The radar-compatible plastic cover component according to claim 1, wherein the surface of the plastic cover component is pre-coated with a primer layer and / or a filler layer and / or electrostatically pre-treated.

16. A manufacturing process for a radar-compatible plastic cover component for a radar device according to claim 1, wherein a colored coating comprising a flaky effect pigment having light-absorbing properties without metallic effect pigments is applied to an optionally pre-treated and / or pre-treated surface of the plastic cover component, the colored coating is applied in a plurality of layers arranged vertically, the absorbing flaky effect pigment is present in each of the layers, at least two of the layers have different geometric layer thicknesses, drying is performed after each of the layers are applied, and the surface of the plastic cover component has no further coloring or metallic coating.

17. The process according to claim 16, wherein the colored coating is applied to a total dry layer thickness in the range of 8 to 25 μm.

18. The process according to claim 16, wherein the colored coating comprises, in each of the layers, a flake-like effect pigment in an amount of 5 to 40% by weight, based on the weight of each of the layers of the colored coating.

19. The process according to claim 16, wherein the application of the colored coating is carried out by a spray process, a roller coating process, a curtain coating process, an in-mold process, or an electrostatic coating process.

20. The process according to claim 19, wherein the application of the colored coating is carried out as a 2 to 4 partial step spray process by continuously applying 2 to 4 layers vertically in each case, the amount of the flake effect pigment having the light-absorbing properties in each of the layers is at least 5% by weight based on the dry weight of each of the layers, and drying is carried out at a temperature of at least 20°C after the application of each of the layers.

21. The process according to claim 16, wherein at least one of the layers of the colored coating has a dry layer thickness of <5 μm.

22. The process according to claim 16, wherein the surface of the plastic cover component is pre-coated with a primer layer and / or a filler layer and / or pre-treated electrostatically.

23. The process according to claim 16, wherein the clear coat is applied as the outermost layer to the surface of the colored coating.

24. The process according to claim 16, wherein the plastic cover component is a plastic plate or film, and the plastic cover component can optionally have a three-dimensional shape.

25. Use of the radar-compatible plastic cover component described in claim 1 as a vehicle component.

26. A vehicle component comprising a radar-compatible plastic cover component as described in claim 1.

Images