Use of a coating formulation comprising a metallic effect pigment for painting vehicles equipped with radar sensors and lidar sensors

Abstract

The present invention relates to the use of a coating formulation comprising a metal effect pigment for coating a vehicle equipped with radar sensors and lidar sensors, wherein the metal effect pigment comprises a metal substrate which is optionally passivated and encapsulated by at least one dielectric layer, the metal effect pigment has an average pigment thickness of 20 nm to 2000 nm and the relative standard deviation of the average pigment thickness is at most 40 %.

Description

Coating formulations containing metallic effect pigments are used for coating vehicles equipped with radar sensors and lidar sensors. Technical Field

[0001] This invention relates to the use of coating formulations containing metallic effect pigments for coating vehicles equipped with radar sensors and lidar sensors. Background Technology

[0002] Modern vehicles, especially motor vehicles, are equipped with multiple sensors that make vehicle control easier and simultaneously increase passenger safety. These sensors are indispensable for autonomous vehicles, which are currently under extensive research. In addition to cameras that record the vehicle's surroundings in a traditional way, these sensors are primarily radar and lidar sensors.

[0003] Radar sensors are used to detect objects in the environment, such as other vehicles or pedestrians, and to measure their distance from vehicles and their relative speed. Radar is an acronym for "radio detection and ranging," meaning radio-based detection and distance measurement. Therefore, radar sensors are sensors based on electromagnetic radiation. Radio waves emitted by a radiation source and reflected from surrounding objects are recorded by the radar sensor. The measured values ​​are converted into electrical signals, which are ultimately evaluated in a specific control device. Although other frequency ranges are possible in principle, radar sensors primarily operate in the 76 GHz to 81 GHz frequency range.

[0004] In contrast, lidar sensors are electromagnetic radiation-based sensors that use light waves to measure distance and velocity. Lidar is an acronym for "light detection and ranging," meaning light-based detection and distance measurement. Light waves emitted by a radiation source are reflected by objects in the field of view. Distance is calculated using so-called combat time, the time it takes for light to travel a certain distance. Like radar sensors, the measured values ​​are converted into electrical signals and ultimately evaluated in a specific control device. Although other wavelengths are possible in principle, lidar sensors primarily operate using near-infrared light with a wavelength of 905 nm.

[0005] Compared to lidar sensors, radar sensors are less sensitive to weather conditions such as rain, snow, or fog. However, tilted reflective surfaces can affect measurement results. Therefore, modern vehicles typically install both radar and lidar sensors to benefit from the advantages of both sensor types. LiDAR sensors must be exposed externally and are usually mounted on the bumper. This is because vehicle paint absorbs or reflects light but does not transmit it. Therefore, lidar sensors cannot be mounted behind panels in the vehicle, which are typically made of plastic and coated with vehicle paint. However, radio waves can penetrate non-conductive materials such as plastic. For aesthetic reasons, radar sensors are often mounted behind such panels in vehicles. However, these panels, including the vehicle paint on them, must not excessively attenuate radio radiation.

[0006] Therefore, in order to achieve the most accurate detection and distance measurement possible, the formulation used for painting vehicles equipped with radar and lidar sensors must have sufficiently high radio wave transmittance and simultaneously sufficiently high light wave reflectance.

[0007] In addition, the corresponding paint formulation must also have a specific color, also known as hue. Many customers desire a particular color for their vehicle paint, while maintaining a bright and vibrant appearance. Besides a specific color, the vehicle paint must also have sufficiently high gloss and hue. Furthermore, vehicle paint with a metallic effect produced by the pigments contained in the paint formulation is considered particularly attractive. In other words, the angular heterochroma of the gloss must also be sufficiently high. Moreover, the vehicle paint needs sufficiently high hiding power. If the hiding power is insufficient, the paint formulation must be applied to the vehicle at a correspondingly greater layer thickness, which, in addition to higher painting costs, also leads to an increase in vehicle weight.

[0008] US2018 / 258293 A1 describes powder coatings and methods for producing powder coatings. WO 2019 / 063372A1 describes gold effect pigments with a hue in the range of 67° to 78° and a chromaticity greater than or equal to 90. US2003 / 059598 A1 describes a coating system and a method of coating a substrate with a powder coating composition comprising a coloring effect pigment. WO 2020 / 208134A1 describes radar-frequency transparent effect pigment mixtures, their formulations, and coatings.

[0009] In existing technologies, carbon black is often added to coating formulations to increase their hiding power. However, this results in a loss of brightness. It also reduces the reflectivity of light waves, which negatively impacts the measurement accuracy of lidar sensors. To achieve sufficiently high hiding power, the proportion of pigments responsible for the metallic effect in the coating formulation can be increased. However, this reduces radio wave transmission, thus negatively affecting the measurement accuracy of radar sensors. This is because the pigments responsible for the metallic effect in the coating formulation have metallic cores. Due to the relatively high polarization ability of metals in an electric field, radio wave attenuation occurs as their proportion increases. Pigments without metallic cores and therefore dielectric can also be used in coating formulations. Pearlescent pigments are mentioned here as an example, which typically contain mica or glass substrates. However, the use of such pigments conflicts with the metallic effect. Furthermore, it is impossible to achieve sufficiently high hiding power with pearlescent pigments. Therefore, carbon black must be added to the corresponding coating formulation. As mentioned earlier, this leads to a loss of brightness and also reduces light wave reflectivity.

[0010] In this regard, new methods are needed to overcome the aforementioned drawbacks of existing coating formulations. Therefore, the object of the present invention is to provide a method that meets the requirements for coating formulations used to paint vehicles equipped with radar sensors and lidar sensors, without adversely affecting color and hiding power. Summary of the Invention

[0011] The above objectives are achieved through the embodiments of the invention as characterized in the claims.

[0012] Therefore, according to the present invention, a coating formulation comprising a metallic effect pigment is provided for use in coating vehicles equipped with radar sensors and lidar sensors, wherein the metallic effect pigment comprises a metal substrate optionally passivated and encapsulated by at least one dielectric layer, the metallic effect pigment having an average pigment thickness of 20 nm to 2000 nm and a relative standard deviation of the average pigment thickness of up to 40%.

[0013] The coating formulation used according to the present invention enables cost-effective painting of vehicles equipped with radar sensors and lidar sensors. The vehicle paint surface obtained from the coating formulation not only possesses sufficiently high light reflectivity and sufficiently high radio wave transmittance, but also features sufficiently high brightness and sufficiently high chromaticity, exhibiting sufficiently high angular anisotropy and simultaneously sufficiently high hiding power. This is due to the inclusion of metallic effect pigments with specific geometric properties in the coating formulation.

[0014] According to the present invention, the coating formulation comprises a metallic effect pigment. Compared with pearlescent pigments having a mica or glass substrate, the metallic effect pigment comprises a metallic substrate. Therefore, the metallic effect pigment has a metallic core. Because of this, the metallic effect pigment can achieve higher hiding power compared to pearlescent pigments. If necessary, the metallic substrate can be passivated. For example, it can be coated with a natural oxide layer.

[0015] Regarding the materials, there are no further limitations on the metal substrate. For example, the metal substrate can be made of metals such as iron, aluminum, copper, nickel, chromium, zinc, tin, silver, gold, platinum, cobalt, lanthanides, and titanium, as well as mixtures or alloys thereof (including steel, particularly stainless steel). In a preferred embodiment, the metal substrate is made of aluminum.

[0016] According to the present invention, the metal substrate is encapsulated by at least one dielectric layer. Generally, it is sufficient if only a portion of the surface of the metal substrate is covered with at least one dielectric layer. For example, only one of the two main surfaces of the metal substrate may be covered with at least one dielectric layer. Furthermore, the side surfaces of the metal substrate may also be excluded. However, according to the present invention, the entire surface of the optionally passivated metal substrate is covered with at least one dielectric layer, which is why we also discuss encapsulation here. This not only helps to improve color effects but also enhances the mechanical and chemical resistance of metallic effect pigments. If more than one dielectric layer is present, each dielectric layer encapsulates the underlying dielectric layer and the underlying metal substrate.

[0017] The at least one dielectric layer is made of a dielectric material. Typically, these are (semi)metal oxides such as silicon dioxide (SiO2) or aluminum oxide (Al2O3), which are considered to have low refractive indexes n ≤ 1.8, and (semi)metal oxides such as iron(III) (Fe2O3), titanium(IV) (TiO2), tin(IV) (SnO2), chromium(III) (Cr2O3), or cobalt(III) (Co2O3), which are considered to have high refractive indexes n > 1.8, but are not limited thereto. Other low- and / or high-refractive-index dielectrics may also be used, for example. By appropriately selecting the dielectric of the at least one dielectric layer, a desired hue can be set, where the layer thickness, in addition to the refractive index of the dielectric, also affects the color. If the layer thickness of the at least one dielectric layer is appropriately set, interference occurs in the visible spectrum, caused by the reflection of incident light at the interface of the at least one dielectric layer. In the case of such metallic effect pigments (also known as interference pigments), the layer thickness of the at least one dielectric layer is typically at least 20 nm. Highly refractive dielectrics are the primary cause of interference and therefore also the primary cause of color.

[0018] To achieve the desired color, a single dielectric layer can also be made of different (highly refractive) dielectrics. A dielectric layer made of iron oxide (III) and titanium oxide (IV) is mentioned here as an example. It is essentially referred to as a hybrid layer.

[0019] In interference pigments, metallic substrates facilitate interference due to reflections occurring on the substrate surface, while pearlescent pigments with mica or glass substrates are naturally not subject to this interference.

[0020] The at least one dielectric layer can be applied to an optionally passivated metal substrate by hydrolytic decomposition of a suitable precursor compound, such as tetraethyl orthosilicate (Si(OC2H5)4), ferric chloride (III) (FeCl3), or ferric nitrate (III) (Fe(NO3)3), followed by tempering if necessary. The at least one dielectric layer can also be applied by gas-phase decomposition of a suitable precursor compound, such as di-tert-butoxydiacetoxysilane (Si(OC(CH3)3)2(OCOCH3)2) or iron pentacarbonyl (Fe(CO)5). These processes are well known to those skilled in the art.

[0021] For example, in EP 1 114 103 B1, a dielectric layer made of silica using sodium silicate is first applied to a metal substrate made of aluminum. Subsequently, a wet chemical coating with iron oxide (III) is performed using ferric chloride (III). Furthermore, a coating with titanium oxide (IV) and tin oxide (IV) is described in EP 1 114 103 B1. A production method is known from EP 0 708 154 B1, which uses a combination of hydrolytic decomposition and gas-phase decomposition to apply the dielectric layer. First, a wet chemical coating of a metal substrate made of aluminum is performed using ammonia as a base and tetraethyl orthosilicate as a precursor compound. After drying the metal substrate coated in this manner, a coating using iron oxide (III) is performed in a fluidized bed reactor, where iron pentacarbonyl is used as the precursor compound. Alternatively, two dielectric layers can be applied in a fluidized bed reactor, in which case, in addition to iron pentacarbonyl, di-tert-butoxydiacetoxysilane is also used as the precursor compound. Finally, a purely wet chemical process for coating a metal substrate made of aluminum with iron oxide (III) using ferric nitrate (III) is known from WO 2013 / 175339A1. Purely wet chemical processes are also described in WO2015 / 014484 A1 and WO 2020 / 038684A1.

[0022] In a specific embodiment, the metallic effect pigment comprises an optionally passivated aluminum substrate coated sequentially with a silicon dioxide dielectric layer and an iron oxide (III) dielectric layer. Instead of the iron oxide (III) dielectric layer, a dielectric layer made of iron oxide (III) and titanium oxide (IV), i.e., a mixed layer, can also be applied to the silicon dioxide dielectric layer. Furthermore, corresponding low-refractive-index and high-refractive-index dielectric layers can also be alternately applied to the metal substrate.

[0023] If desired, metallic effect pigments may be provided with a surface coating. Not limited to this, the surface coating may be made of organic polymers, silanes, or siloxanes. The mechanical and chemical resistance of metallic effect pigments can be further increased by applying such a surface coating to at least one dielectric layer (also known as surface functionalization). The respective processes are described in detail in WO 2015 / 044188 A1 and EP 2318 463B1, etc.

[0024] According to the present invention, the metallic effect pigment has an average pigment thickness of 20 nm to 2000 nm, preferably 50 nm to 1700 nm, and even more preferably 200 nm to 1500 nm. In this context, the term "pigment thickness" refers to the thickness of the entire metallic effect pigment, that is, including the thickness of at least one dielectric layer and the thickness of any surface coating that may have been applied thereon.

[0025] The average pigment thickness was determined by measurement based on scanning electron microscopy (SEM) images. The process involved dispersing the metallic effect pigment in powder form in a nitrocellulose-based coating and applying it to aluminum foil. The powder-to-coating mixing ratio in the liquid system was 1:10. A 1 cm section coated in this manner was ablated using a wide-beam ion source and irradiated with high-energy Ar ions. 2 The aluminum foil portion was cut to create a cross-section. To ensure sufficient conductivity, the cut cross-section was sputtered with a 5 nm thin carbon layer. The cross-section of the metallic effect pigment was then imaged using a scanning electron microscope at magnifications from 10,000 to 30,000. The pigment thickness was determined from at least 500 different metallic effect pigments. The average pigment thickness was then calculated as the arithmetic mean of the measured pigment thicknesses.

[0026] According to the invention, the relative standard deviation of the average pigment thickness is at most 40%, preferably at most 20%, and even more preferably at most 10%. The relative standard deviation, also known as the coefficient of variation, relates the absolute standard deviation to the average pigment thickness measured from at least 500 different metallic effect pigments. Therefore, the relative standard deviation of the average pigment thickness is a measure of the thickness variation of the metallic effect pigment. The smaller the relative standard deviation, the smaller the thickness variation of the metallic effect pigment.

[0027] The invention is not further limited in terms of the size of metallic effect pigments, i.e., their pigment diameter. Typically, metallic effect pigments have a pigment diameter d of 3 μm to 100 μm, for example 5 μm to 50 μm, or 10 μm to 30 μm. 50 In this case, the pigment diameter is called d. 50 This indicates that 50% of the metallic effect pigments in the sample have values ​​lower than the specified value. At least 500 different metallic effect pigments are also included as samples.

[0028] Pigment diameter d 50 The particle size was determined based on laser diffraction using a commercially available particle size analyzer from Sympatec GmbH, Clausthal-Zellerfeld, Germany, in accordance with DIN ISO 13320:2020-01.

[0029] The aspect ratio of metallic effect pigments can ultimately be determined by the average pigment thickness and the pigment diameter d. 50 Determined. Aspect ratio, i.e., pigment diameter d. 50 The ratio to the average pigment thickness is preferably at least 3:1, for example at least 4:1, or at least 5:1. A large aspect ratio improves the alignment of metallic pigments when the paint formulation is applied to the vehicle surface, which has a particularly advantageous effect on the hiding power of the vehicle paint produced by the paint formulation.

[0030] Due to the specific geometric properties of metallic effect pigments, the vehicle paint produced by the coating formulation possesses not only sufficiently high light reflectivity and sufficiently high radio wave transmittance, but also sufficiently high brightness and sufficiently high chromaticity, sufficiently high brightness anisochromaticity with angle, and simultaneously sufficiently high hiding power. As the inventors have surprisingly discovered, this is particularly attributable to the small thickness variation of the metallic effect pigments contained in the coating formulation, expressed as a relative standard deviation of the average pigment thickness, and at most 40%, preferably at most 20%, and even more preferably at most 10%.

[0031] Because at least one dielectric layer can be applied to the metal substrate with high precision in terms of its layer thickness, the thickness variation of the metallic effect pigment depends primarily on the thickness variation of the metal substrate used in its production. In the case of a metal substrate with small thickness variation, a metallic effect pigment with small thickness variation is thus obtained after at least one dielectric layer has been applied. This also applies if another surface coating is applied to at least one dielectric layer. Conversely, a metal substrate with large thickness variation results in a metallic effect pigment with large thickness variation. The thickness difference of the metal substrate is transferred to some extent to the at least one dielectric layer applied thereon and optionally to the surface coating applied thereon.

[0032] In order to meet the requirement that the relative standard deviation of the average pigment thickness is at most 40%, preferably at most 20%, or even more preferably at most 10%, a metallic substrate with the smallest possible thickness variation must be used in the production of metallic effect pigments.

[0033] For example, vacuum metallization can yield metal substrates with minimal thickness variation. Vacuum metallization is a specific form of physical vapor deposition (PVD). For this purpose, a metal vapor-deposited support film, such as aluminum, is deposited under high vacuum to create a thin metal layer on the support film with a thickness in the nanometer range. The metal layer is then removed from the support film with the aid of a solvent, where it is pulverized into flakes by the generated shear force. To facilitate separation, a stripping coating can be applied to the support film prior to vapor deposition. Metal substrates obtained by vacuum metallization are characterized by exceptionally small thicknesses. Consequently, their thickness variation is also exceptionally low, which is why the resulting metallic effect pigments meet a relative standard deviation of at most 40%, preferably at most 20%, and even more preferably at most 10% for the average pigment thickness.

[0034] In contrast, metal substrates obtained by wet milling exhibit significantly more pronounced thickness variations, resulting in a considerably larger relative standard deviation of the average pigment thickness. Based on their appearance, metal substrates obtained by wet milling are also referred to as "cornflakes" or "dollars." While "cornflake" type (also known as flake-type) metal substrates have irregular and serrated side edges, the side edges in "dollar" type (also known as lens-type) metal substrates are typically rounded. Metal substrates obtained by vacuum metallization, also known as "vacuum metallized pigments," abbreviated as VMP, are polygons with straight side edges. Compared to "cornflake" and "dollar" type metal substrates, they have significantly smoother surfaces, in addition to their particularly small thickness variations. In a preferred embodiment, the metal substrate is a metal substrate obtained by vacuum metallization.

[0035] The coating formulations according to the invention for painting vehicles equipped with radar sensors and lidar sensors may contain a mixture of two or more metallic effect pigments. When referring to metallic effect pigments in the present context, it means metallic effect pigments having the aforementioned specific geometric properties, particularly small thickness variations. By using a mixture of two or more metallic effect pigments, it is also possible to achieve hues that are not easily obtained using a single metallic effect pigment. For this purpose, in addition to metallic effect pigments, the coating formulation may also contain at least one other pigment, including mica-based or glass-based pearlescent pigments. However, the pigments included in the coating formulation may also be limited to metallic effect pigments, i.e., the coating formulation does not contain any other pigments besides metallic effect pigments. In particular, the coating formulation preferably does not contain organic or inorganic absorbing pigments, such as carbon black, or contains at most a small proportion of absorbing pigments. As mentioned at the beginning, the addition of carbon black is accompanied by a loss of brightness. Light reflectivity is also reduced, which negatively impacts the measurement accuracy of lidar sensors. Due to their sufficiently high opacity (which will be discussed in more detail below), the coating formulations used according to the invention do not require the addition of carbon black or the like, or at most only a small amount.

[0036] In addition to pigments, coating formulations also contain binders and solvents, and may also contain other components such as fillers and / or additives. Typical binders and solvents, as well as any kind of fillers and additives, are known to those skilled in the art. Small flakes made of calcium carbonate (CaCO3) are mentioned herein as an exemplary filler. Examples of additives include defoamers, wetting agents, light stabilizers, and leveling agents.

[0037] The paint coating is ultimately formed by evaporating the solvent after the paint formulation is applied to the vehicle surface. The application of the paint formulation is not limited to a specific method. This is advantageously carried out by spraying or spraying with a pressure atomizer, wherein the layer thickness of the vehicle paint coating produced by the paint formulation can be adjusted by the duration of application. Because the paint formulation results in sufficiently high hiding power, a relatively small layer thickness is sufficient for the vehicle paint coating. Typical layer thicknesses are 10 μm to 30 μm, although even smaller layer thicknesses are possible, provided the hiding power is sufficiently high. A layer thickness of 14 μm is mentioned herein as an example. Here, layer thickness always refers to the layer thickness of the vehicle paint coating, which is reduced compared to the layer thickness of the paint formulation by drying the solvent contained therein and optionally by film formation.

[0038] The pigment concentration of metallic effect pigments in paint formulations is typically between 1% and 15% by mass, but is not limited to this. Pigment concentration refers to the mass fraction of the metallic effect pigment relative to the total dry mass of the paint formulation. In addition to the mass of the metallic effect pigment, the total dry mass also includes the mass of all other non-volatile components. The following applies: the higher the pigment concentration, the higher the hiding power for the same thickness of vehicle paint layer.

[0039] The paint formulation according to the invention for coating vehicles equipped with radar sensors and lidar sensors has sufficiently high hiding power. Typically, for a vehicle paint finish with a layer thickness of 14 μm produced by a paint formulation in which the metallic effect pigment has a pigment mass concentration of 1% to 15% by mass, the color distance ΔE110° is at most 1.5, preferably at most 1.2, and even more preferably at most 1.0. The color distance ΔE110° is a measure of hiding power, where a smaller color distance indicates higher hiding power. In this case, a paint finish with a maximum color distance ΔE110° of 1.5 is described as opaque.

[0040] To determine the hiding power, a paint formulation was applied to a black and white panel, resulting in a vehicle paint finish with a layer thickness of 14 μm. The color distance between black and white was then measured in a 45° / 110° geometry using a commercially available multi-angle spectrophotometer, according to DIN 6175:2019-07.

[0041] The hue of a vehicle paint finish produced by a coating formulation depends primarily on the color characteristics of the metallic effect pigments contained in the formulation, but is also influenced by added pigments such as mica- or glass-based pearlescent pigments and other organic or inorganic absorbent pigments. This also applies to brightness and chromaticity, as well as brightness anisochromaticity with angle. Hue H uv An exemplary value for 15° (also known as the hue angle) is 25 to 50, which is typical for red, orange, or gold hues. However, hues are by no means limited to this. Therefore, the hue angle can also be outside the range of 25 to 50. In terms of lightness and chromaticity, lightness L*15° is typically at least 100, and chromaticity C... uv 15° is typically at least 150. The luminance anisochromaticity with angle, expressed as the Alman index FI, is typically at least 20.

[0042] To determine hue, brightness, chromaticity, and luminance anisochromaticity with respect to angle, a paint formulation was applied to a black background. Then, for a 10° observer, the spectral reflectance of a beam of light incident at a 45° angle on the measurement surface and emitted from a D65 light source was measured using a commercially available multi-angle spectrophotometer at six different detection angles (-15°, 15°, 25°, 45°, 75°, and 110°), according to DIN EN ISO 18314-3:2018-12, and converted to the corresponding variables in the CIELAB and CIEHLC color spaces. The commercially available multi-angle spectrophotometer used here was the "BYK-mac i MetallicColour" device from BYK-Gardner GmbH, Geretsried, Germany, which is also used to determine the color distance ΔE110°. The Alman color index FI with respect to angle was calculated according to ABJ Rodrigues, “Metallic flop and its measurement”, J. Oil Color Chem. Assoc. 1992, 75(4), 150-153.

[0043] The coating formulation according to the present invention for painting vehicles equipped with radar sensors and lidar sensors has sufficiently high light reflectivity and sufficiently high radio wave transmittance. Currently, the dielectric constant (also known as permittivity ε) is used to characterize radio wave transmittance, as described in F. Pfeiffer, “Analyse und Optimierung von Radomen für automobile Radarsensoren”, dissertation, Technical University of Munich, 2009. The smaller the dielectric constant ε, the less radio wave attenuation. Typically, the vehicle paint surface produced by the coating formulation has a dielectric constant ε of up to 30, preferably up to 20, and even more preferably up to 10 in the frequency range of 76 GHz to 81 GHz. With such a dielectric constant, the coating formulation is particularly suitable for painting vehicles equipped with radar sensors. Furthermore, the vehicle paint surface produced by the coating formulation typically has a reflectivity R of at least 50%, preferably at least 60%, and even more preferably at least 70% at a wavelength of 905 nm. With such reflectivity, the coating formulation is particularly suitable for coating vehicles equipped with lidar sensors.

[0044] The dielectric constant ε was determined using a commercially available radome scanner in the frequency range of 76 GHz to 81 GHz. After calibration, measurements were taken on a 2 mm thick polycarbonate measuring plate before and after the application of the coating formulation. In both cases, a radio wave beam was irradiated perpendicularly to the surface of the measuring plate. The dielectric constant ε can ultimately be determined from the measured values, thus remaining constant within the selected frequency range in this application. The commercially available radome scanner used herein is the "Radome Measurement System" from perisens GmbH, Feldkirchen, near Munich, Germany. The reflectivity R was similarly determined at a wavelength of 905 nm by irradiating the surface with light perpendicular to it.

[0045] The coating formulation can be advantageously used for painting motor vehicles, particularly self-propelled motor vehicles equipped with radar sensors and lidar sensors. However, in principle, any vehicle can be painted with the coating formulation used according to the invention.

[0046] The coating formulation used according to the present invention achieves cost-effective painting of vehicles equipped with radar sensors and lidar sensors. The vehicle paint produced by the coating formulation not only possesses sufficiently high light reflectivity and sufficiently high radio wave transmittance, but also features sufficiently high brightness and sufficiently high chromaticity, exhibiting sufficiently high angular heterochromaticity and simultaneously sufficiently high hiding power. Therefore, the coating formulation used according to the present invention satisfies the requirements for coating formulations used in painting vehicles equipped with radar sensors and lidar sensors without adversely affecting color and hiding power. Detailed Implementation Examples

[0047] The following examples are provided to further illustrate the present invention, but are not limited thereto.

[0048] Paint formulations having the metallic effect pigments listed in Table 1 are referred to as pigments a through e, all of which are commercially available.

[0049] Pigments a and b were sourced from Schlenk Metallic Pigments GmbH, Roth, Germany, while pigments c, d, and e were sourced from BASF Colors & Effects GmbH, Ludwigshafen, Germany. The metallic effect pigments, along with the average pigment thickness and its absolute standard deviation, as well as the relative standard deviation of the average pigment thickness, as determined by the aforementioned measurement methods, are listed in Table 1. All metallic effect pigments in Table 1 involve aluminum-based metal substrates. In the cases of pigments a and b, the aluminum substrate was obtained by vacuum metallization, while in the cases of pigments c, d, and e, it was obtained by wet milling. In pigments c and d, the aluminum substrate has a "cornflake" shape, while in pigment e, the aluminum substrate has a "dollar" shape.

[0050] Table 1

[0051]

[0052] To prepare coating formulations, the metallic effect pigments listed in Table 1 were dispersed in a coating system (a single-component coating based on cellulose acetobutyrate, containing a solvent). In each coating formulation, the metallic interference pigments used were either present alone as pure hues or as a mixture, and optionally with carbon black paste (from Helio Beit Pigmentpasten GmbH, Cologne, Germany) as one or more other pigments. UN 907) and / or red pigment paste (from Clariant AG, Muttenz, Switzerland). Red A-P2Y 100-ST exists together.

[0053] After preparing the coating formulations, they were sprayed onto a polycarbonate measuring plate to obtain a coating with a thickness of 14 μm after solvent evaporation. The radio transmittance and light reflectance of the paint surface, as well as their color and hiding power, were then examined in more detail. The corresponding variables were determined according to the measurement methods mentioned above.

[0054] Examples 1 to 4:

[0055] In the hue angle range of 33 to 35 H uv 15° with orange shading paint finish

[0056] Table 2 shows the pigment mass concentration (PMK) for each paint finish, excluding the metallic effect pigments used. 颜料 In addition, the pigment mass concentrations (PMK) of other pigments (if present) are shown. w.颜料 Furthermore, Table 2 includes the dielectric constant ε, reflectivity R at a wavelength of 905 nm, and hue H for each paint finish in the frequency range of 76 GHz to 81 GHz. uv 15°, brightness L*15°, chromaticity C uv The measured values ​​of 15°, Alman's color difference index FI with angle, and color distance ΔE110°.

[0057] Table 2

[0058]

[0059] *The carbon black paste described above is used here as other pigments.

[0060] The hue angle H corresponding to the orange shading is in the range of 33 to 35. uv The 15° is almost entirely derived from the metallic effect pigments used.

[0061] In the presence of pigment a Example 1 In this process, 12% PMK by mass is required. 颜料 The pigment mass concentration is adjusted to achieve an opaque state with a layer thickness of 14 μm.

[0062] In the presence of pigment c (not according to the invention) Example 2 In the same layer thickness, the pigment mass concentration PMK 颜料 It is also 12% mass. However, an opaque state was not achieved. The Alman chromaticity index FI with angle also decreased.

[0063] In the presence of pigment c (not according to the invention) Example 3 In the same layer thickness, the pigment mass concentration PMK 颜料 This increases the mass percentage to 13.42%, thus achieving an opaque state. However, this increases the dielectric constant ε to a value exceeding 30 in the frequency range of 76 GHz to 81 GHz.

[0064] Conversely, in the presence of pigment c (not according to the invention) Example 4 In this process, carbon black paste is added to achieve an opaque state. However, as can be seen from the comparison with Example 1, this comes at the cost of color. As a result, the reflectance R at a wavelength of 905 nm drops to a value of less than 50%.

[0065] Based on Examples 1 to 4, it can be concluded that only by using a coating formulation containing pigment a can a vehicle paint surface be obtained that has not only sufficiently high light reflectivity and sufficiently high radio wave transmittance, but also sufficiently high brightness and sufficiently high chromaticity, as well as sufficiently high brightness angular heterochromaticity and sufficiently high hiding power.

[0066] Examples 5 to 8:

[0067] In the hue angle range of 33 to 35 H uv 15° with orange shading paint finish

[0068] Table 3 shows the pigment mass concentration (PMK) for each paint finish, except for the metallic effect pigments used. 颜料 In addition, the pigment mass concentrations (PMK) of other pigments (if present) are shown. w.颜料 Furthermore, for each paint finish, Table 3 includes the dielectric constant ε, reflectivity R at a wavelength of 905 nm, and hue H within the frequency range of 76 GHz to 81 GHz. uv 15°, brightness L*15°, chromaticity C uv The measured values ​​of 15°, Alman's color difference index FI with angle, and color distance ΔE110°.

[0069] Table 3

[0070]

[0071] *The carbon black paste described above is used here as other pigments.

[0072] The hue angle H corresponding to the orange shading is in the range of 33 to 35. uv The 15° is almost entirely derived from the metallic effect pigments used.

[0073] In the presence of pigment a Example 5 In this process, 12% PMK by mass is required. 颜料 The pigment mass concentration was adjusted to achieve an opaque state with a layer thickness of 14 μm. Example 5 was the same as Example 1.

[0074] In the presence of pigment e (not according to the invention) Example 6 In the same layer thickness, the pigment mass concentration PMK 颜料 It is also 12% mass. However, an opaque state was not achieved. The Alman chromaticity index FI with angle also decreased.

[0075] In the presence of pigment e (not according to the invention) Example 7 In the same layer thickness, the pigment mass concentration PMK 颜料This increases the mass percentage to 19.03%, thus achieving an opaque state. However, this increases the dielectric constant ε to a value exceeding 30 in the frequency range of 76 GHz to 81 GHz.

[0076] Conversely, in the presence of pigment e (not according to the invention) Example 8 In this process, carbon black paste is added to achieve an opaque state. However, as can be seen from the comparison with Example 5, this comes at the cost of color. As a result, the reflectivity R at a wavelength of 905 nm drops to a value of less than 50%.

[0077] Based on Examples 5 to 8, it can be concluded that only by using a coating formulation containing pigment a can a vehicle paint surface be obtained that has not only sufficiently high light reflectivity and sufficiently high radio wave transmittance, but also sufficiently high brightness and sufficiently high chromaticity, as well as sufficiently high brightness angular heterochromaticity and sufficiently high hiding power.

[0078] Examples 9 to 12:

[0079] In the hue angle range of 47 to 48 H uv 15° with a golden tint of paint

[0080] Table 4 shows the pigment mass concentration (PMK) for each paint finish, excluding the metallic effect pigments used. 颜料 In addition, the pigment mass concentrations (PMK) of other pigments (if present) are shown. w.颜料 Furthermore, for each paint finish, Table 4 includes the dielectric constant ε and hue H in the frequency range of 76 GHz to 81 GHz. uv 15°, brightness L*15°, chromaticity C uv The measured values ​​of 15°, Alman's color difference index FI with angle, and color distance ΔE110°.

[0081] Table 4

[0082]

[0083] *The carbon black paste described above is used here as other pigments.

[0084] The hue angle H corresponding to the golden shading is in the range of 47 to 48. uv The 15° is almost entirely derived from the metallic effect pigments used.

[0085] In a mixture containing pigment a and pigment b Example 9 In this process, 6.865% by mass of PMK is required. 颜料 The pigment mass concentration is adjusted to achieve an opaque state with a layer thickness of 14 μm. Pigment a and pigment b exist in a 50:50 mass ratio.

[0086] In having pigment d (not according to the invention) Example 10 In the same layer thickness, the pigment mass concentration PMK 颜料 It also has a mass percentage of 6.865%. However, it did not achieve an opaque state. The Alman color variation index (FI) with angle also decreased.

[0087] In having pigment d (not according to the invention) Example 11 In the same layer thickness, the pigment mass concentration PMK 颜料 This increases the mass percentage to 11.637%, thus achieving an opaque state. However, this increases the dielectric constant ε to a value exceeding 30 in the frequency range of 76 GHz to 81 GHz.

[0088] Conversely, in the presence of pigment d (not according to the invention) Example 12 In this process, carbon black paste is added to achieve an opaque state. However, as can be seen from the comparison with Example 9, this comes at the cost of sacrificing color.

[0089] Based on Examples 9 to 12, it can be concluded that only by using a coating formulation containing pigment a and pigment b can a vehicle paint surface be obtained that has not only sufficiently high light reflectivity and sufficiently high radio wave transmittance, but also sufficiently high brightness and sufficiently high chromaticity, as well as sufficiently high brightness angular heterochromaticity and sufficiently high hiding power.

[0090] Examples 13 to 16:

[0091] In the hue angle range of 27 to 28 H uv 15° with reddish tint

[0092] Table 5 shows the pigment mass concentration (PMK) for each paint finish, except for the metallic effect pigments used. 颜料 In addition, the pigment mass concentrations (PMK) of other pigments (if present) are shown. w.颜料 Furthermore, for each paint finish, Table 5 includes the dielectric constant ε, reflectivity R at a wavelength of 905 nm, and hue H within the frequency range of 76 GHz to 81 GHz. uv 15°, brightness L*15°, chromaticity C uv The measured values ​​of 15°, Alman's color difference index FI with angle, and color distance ΔE110°.

[0093] Table 5

[0094]

[0095] *The carbon black paste and the red pigment paste described above are used here as other pigments. The values ​​in the left column each represent the pigment mass concentration of the carbon black paste, while the values ​​in the right column each represent the pigment mass concentration of the red pigment paste.

[0096] The hue angle H corresponding to the red shading is in the range of 27 to 28. uv 15° comes from a combination of metallic effect pigments used with red pigment paste.

[0097] In the presence of pigment a Example 13 In this process, 12.052% by mass of PMK is required. 颜料 The pigment mass concentration is adjusted to achieve an opaque state with a layer thickness of 14 μm.

[0098] Using pigment a Example 14 In the same layer thickness, the pigment mass concentration PMK 颜料 To achieve opacity, carbon black paste was added. However, as can be seen from the comparison with Example 13, this comes at the cost of color. As a result, the reflectance R at a wavelength of 905 nm also decreased to less than 50%.

[0099] In the presence of pigment e (not according to the invention) Example 15 and having pigment c (not according to the invention) Example 16 In order to achieve an opaque state, a considerable amount of carbon black paste must be added for the same layer thickness. However, as can be seen from the comparison with Example 13, this comes at the cost of color. As a result, the reflectivity R at a wavelength of 905 nm also drops to less than 50%.

[0100] Based on Examples 13 to 16, it can be concluded that only by using a coating formulation containing pigment a can a vehicle paint surface be obtained that has not only sufficiently high light reflectivity and sufficiently high radio wave transmittance, but also sufficiently high brightness and sufficiently high chromaticity, as well as sufficiently high brightness angular heterochromaticity and sufficiently high hiding power.

Claims

1. A coating formulation comprising a metallic effect pigment for use in coating vehicles equipped with radar sensors and lidar sensors, wherein the metallic effect pigment comprises a metallic substrate encapsulated by at least one dielectric layer and optionally passivated, wherein the metallic substrate is made of a metal selected from iron, aluminum, copper, nickel, chromium, zinc, tin, silver, gold, platinum, cobalt, lanthanides and titanium, or mixtures thereof or alloys thereof, wherein the at least one dielectric layer has a dielectric material selected from silicon dioxide, aluminum oxide, iron(III), titanium(IV), tin(IV), chromium(III) oxide and cobalt(III), and wherein the metallic effect pigment has an average pigment thickness of 200 nm to 1500 nm and the relative standard deviation of the average pigment thickness is at most 40%.

2. The use according to claim 1, wherein the metal substrate is made of aluminum.

3. The use according to claim 1 or 2, wherein the metallic effect pigment is an interference pigment.

4. The use according to any one of claims 1 to 3, wherein the metallic effect pigment is provided with a surface coating.

5. The use according to any one of claims 1 to 4, wherein the relative standard deviation of the average pigment thickness is at most 10%.

6. The use according to any one of claims 1 to 5, wherein the metallic effect pigment has a pigment diameter d of 3 µm to 100 µm. 50 .

7. The use according to any one of claims 1 to 6, wherein the metal substrate is a metal substrate obtained by vacuum metallization.

8. The use according to any one of claims 1 to 7, wherein the coating formulation comprises a mixture of two or more of the said metallic effect pigments.

9. The use according to any one of claims 1 to 8, wherein, in addition to the metallic effect pigment, the coating formulation further comprises at least one other pigment.

10. The use according to any one of claims 1 to 9, wherein the coating formulation does not contain any carbon black.

11. The use according to any one of claims 1 to 10, wherein for a vehicle paint layer with a thickness of 14 μm produced by the coating formulation having a pigment mass concentration of the metallic effect pigment in the coating formulation of 1% to 15% by mass, the color distance ΔE110° is at most 1.

5.

12. The use according to claim 11, wherein the vehicle paint finish produced by the coating formulation has a hue H of 25 to 50. uv 15°, at least 100 lux (L) 15°, at least 150 chromaticity C uv 15° and an Alman color index (FI) of at least 20 with respect to angle.

13. The use according to claim 11 or 12, wherein the vehicle paint finish produced by the coating formulation has a dielectric constant of up to 30 in the frequency range of 76 GHz to 81 GHz. It also has a reflectivity of at least 50% at a wavelength of 905 nm.

14. The use according to any one of claims 1 to 13, wherein the vehicle is a motor vehicle.

15. The use according to claim 14, wherein the motor vehicle is a self-propelled motor vehicle.

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