Use of paint formulations containing metallic effect pigments in painting vehicles equipped with radar and lidar sensors

Abstract

The present invention relates to the use of paint formulations containing metallic effect pigments in the painting of vehicles equipped with radar and lidar sensors, the metallic effect pigments comprising a metal substrate, optionally passivated and coated with at least one dielectric layer, the metallic effect pigments having an average pigment thickness of 20 nm to 2000 nm, the relative standard deviation of said average pigment thickness being at most 40%.

Description

[Technical Field]

[0001] The present invention relates to the use of paint formulations containing metallic effect pigments in the painting of vehicles equipped with radar and lidar sensors. [Background technology]

[0002] Modern vehicles, especially automobiles, are equipped with numerous sensors to facilitate vehicle control and at the same time increase the safety of occupants. Such sensors are essential for autonomous vehicles, which are the subject of much research. In addition to cameras that record the vehicle's surroundings in a traditional way, these are primarily radar and lidar sensors.

[0003] Radar sensors are used to detect objects in the environment, such as other vehicles or pedestrians, and measure their distance from these vehicles and their relative speed. Radar is an abbreviation for "radio detection and ranging." A radar sensor is therefore a sensor based on electromagnetic radiation. Radio waves are emitted by a radiation source and the waves reflected by surrounding objects are registered by the radar sensor. The measured values ​​are then converted into electrical signals that are finally evaluated in a special control device. Radar sensors mainly operate in the frequency range from 76 GHz to 81 GHz, although other frequency ranges are possible in principle.

[0004] In contrast, lidar sensors are sensors based on electromagnetic radiation and use light waves to measure distance and speed. Lidar is an abbreviation for "light detection and ranging." Light waves emitted by a radiation source are reflected by objects within the field of view. The distance is calculated from the so-called time of flight, i.e., the time it takes for light to propagate a certain distance. As with radar sensors, the measured values ​​are converted into electrical signals that are finally evaluated in a special control unit. Lidar sensors mainly operate in the near-infrared, with a wavelength of 905 nm, although other wavelengths are possible in principle.

[0005] Compared to lidar sensors, radar sensors are less affected by weather conditions such as rain, snow, or fog. However, oblique reflective surfaces can affect measurement results. Therefore, modern vehicles often have both radar and lidar sensors installed to take advantage of the benefits of both sensor types. Lidar sensors must be exposed to the outside and are typically mounted on the bumper. This is because vehicle paint absorbs or reflects light rays but does not transmit them. As a result, they are typically made of plastic, and lidar sensors cannot be mounted behind painted vehicle panels. However, radio beams can penetrate non-conductive materials such as plastic. For aesthetic reasons, radar sensors are typically mounted behind such vehicle panels. However, such panels, including the vehicle paint thereon, must not excessively attenuate radio emissions.

[0006] Therefore, for the most accurate detection and distance measurement possible, formulations for painting vehicles equipped with radar and lidar sensors must have a sufficiently high transmittance for radio waves and at the same time a sufficiently high reflectance for light waves.

[0007] Furthermore, the corresponding paint formulation must also have a specific color, also known as coloristics. Many customers desire vehicle paints in a specified color that appears bright and colorful at the same time. In addition to the specified color, the vehicle paint must also have a sufficiently high value and a sufficiently high saturation. Furthermore, vehicle paints in which the pigments contained in the paint formulation produce a metallic effect are perceived as particularly attractive. In other words, the value flop must also be sufficiently high. Furthermore, the vehicle paint must have a sufficiently high covering power. If the covering power is not high enough, the paint formulation must be applied to the vehicle in a correspondingly large layer thickness, which not only increases the painting cost but also increases the vehicle weight.

[0008] Patent document 1 describes a powder coating and a method for making the same. Patent document 2 describes a gold effect pigment having a hue in the range of 67° to 78° and a chroma of 90 or greater. Patent document 3 describes a coating system and a method for coating a substrate with a powder coating composition containing colored effect pigments. Patent document 4 describes a radar frequency-transparent effect pigment mixture, and formulations and coatings thereof.

[0009] In the prior art, carbon black is often added to paint formulations to increase their covering power. However, this is accompanied by a loss of brightness. This also reduces the reflectivity of light waves, adversely affecting the measurement accuracy of lidar sensors. To achieve sufficiently high covering power, the proportion of pigments involved in the metallic effect in the paint formulation can be increased. However, this reduces radio wave transmittance and adversely affects the measurement accuracy of radar sensors. This is because the pigments involved in the metallic effect in the paint formulation have a metal core. Due to the relatively high polarization ability of metals in an electric field, increasing their proportion causes radio wave attenuation. Pigments that do not have a metal core and are therefore dielectric can also be used in paint formulations. Examples include pearlescent pigments, which generally contain mica or glass substrates. However, the use of such pigments contradicts the metallic effect. Furthermore, it is impossible to achieve sufficiently high covering power with pearlescent pigments. Therefore, carbon black must be added to the corresponding paint formulation. As mentioned at the beginning, this leads to a loss of brightness and a decrease in light wave reflectivity. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] U.S. Patent Application Publication No. 2018 / 258293 [Patent Document 2] International Publication No. 2019 / 063372 [Patent Document 3] U.S. Patent Application Publication No. 2003 / 059598 [Patent Document 4] International Publication No. 2020 / 208134 Summary of the Invention [Problem to be solved by the invention]

[0011] In this respect, a new approach is needed to overcome the above-mentioned disadvantages arising from prior art paint formulations. It is therefore an object of the present invention to provide a way to meet the requirements of paint formulations for use in painting vehicles equipped with radar and lidar sensors without adversely affecting color properties and covering power. [Means for solving the problem]

[0012] The above objects are achieved by the embodiments of the invention characterized in the claims.

[0013] Therefore, according to the present invention there is provided the use of a paint formulation containing metallic effect pigments for painting vehicles equipped with radar and lidar sensors, wherein the metallic effect pigments comprise a metal substrate, optionally passivated and coated with at least one dielectric layer, and wherein the metallic effect pigments have an average pigment thickness of 20 nm to 2000 nm, and the relative standard deviation of said average pigment thickness is at most 40%.

[0014] The paint formulation used according to the invention allows for the cost-effective painting of vehicles equipped with radar and lidar sensors, and the vehicle paint obtained from this paint formulation not only has a sufficiently high light wave reflectance and a sufficiently high radio wave transmittance, but is also characterized by a sufficiently high lightness and a sufficiently high saturation, and has a sufficiently high covering power at the same time as a sufficiently high lightness flop, due to the metallic effect pigments contained in the paint formulation, which have specific geometric properties.

[0015] According to the present invention, the paint formulation contains metal effect pigments.In contrast to pearlescent pigments that contain mica or glass substrates, metal effect pigments contain metal substrates.Therefore, metal effect pigments have a metal core.For this reason, metal effect pigments can achieve higher covering power compared to pearlescent pigments.If necessary, the metal substrate is passivated.For example, it can be covered with a natural oxide layer.

[0016] As far as the material is concerned, the metal substrate is not further limited here. 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, especially stainless steel. In a preferred embodiment, the metal substrate is made of aluminum.

[0017] According to the present invention, the metal substrate is coated with at least one dielectric layer. Generally, it is sufficient for only a portion of the surface of the metal substrate to be 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. Additionally, the side surfaces of the metal substrate may be omitted. However, according to the present invention, the entire surface of the optionally passivated metal substrate is covered with at least one dielectric layer, and therefore the term "coating" is used herein. This not only contributes to improved color properties, but also increases the mechanical and chemical resistance of the metallic effect pigment. When two or more dielectric layers are present, each dielectric layer covers the dielectric layer below it and the underlying metal substrate.

[0018] At least one dielectric layer is made of a dielectric. Typically, these are (semi)metal oxides considered to have a low refractive index (n≦1.8), such as silicon dioxide (SiO2) or aluminum oxide (Al2O3), or (semi)metal oxides considered to have a high refractive index (n>1.8), such as, but not limited to, iron(III) oxide (Fe2O3), titanium(IV) oxide (TiO2), tin(IV) oxide (SnO2), chromium(III) oxide (Cr2O3), or cobalt(III) oxide (Co2O3). For example, other low- and / or high-refractive-index dielectrics can also be used. The desired hue can be achieved by appropriately selecting the dielectric for the at least one dielectric layer. In addition to the refractive index of the dielectric, its thickness also influences the color characteristics. By appropriately selecting the thickness of the at least one dielectric layer, interference occurs in the visible spectral range due to the reflection of incident light at the interfaces of the at least one dielectric layer. In the case of such metallic effect pigments, also called interference pigments, the layer thickness of the at least one dielectric layer is typically at least 20 nm. The high refractive index dielectric plays a major role in the interference and thus the color properties.

[0019] A single dielectric layer can also be made from different (high refractive index) dielectrics to set the desired color. A dielectric layer made from iron(III) oxide and titanium(IV) oxide is taken as an example here. This is essentially called a mixed layer.

[0020] In interference pigments, the metal substrate contributes to the interference due to reflections that occur at the substrate surface, which is of course not the case for pearlescent pigments that include mica or glass substrates.

[0021] The at least one dielectric layer can be applied to the optionally passivated metal substrate by hydrolysis of a suitable precursor compound, such as tetraethyl orthosilicate (Si(OC2H5)4), iron(III) chloride (FeCl3) or iron(III) nitrate (Fe(NO3)3), optionally with subsequent tempering. The at least one dielectric layer can also be applied by gas-phase decomposition of a suitable precursor compound, such as di-tert-butoxy-diacetoxysilane (Si(OC(CH3)3)2(OCOCH3)2) or iron pentacarbonyl (Fe(CO)5). The relevant procedures are well known to those skilled in the art.

[0022] In EP 1114103, for example, a dielectric layer made of silicon dioxide using sodium silicate is first applied to a metal substrate made of aluminum. This is followed by a wet-chemical coating with iron(III) oxide using iron(III) chloride. Furthermore, coatings with titanium(IV) oxide and tin(IV) oxide are described in EP 1114103. From EP 0708154, a manufacturing method is known that uses a combination of hydrolysis and gas-phase decomposition to apply a dielectric layer. First, a metal substrate made of aluminum is wet-chemically coated with silicon dioxide using ammonia as the base and tetraethyl orthosilicate as the precursor compound. After drying the coated metal substrate, it is coated with iron(III) oxide in a fluidized-bed reactor using iron pentacarbonyl as the precursor compound. Alternatively, both dielectric layers can be applied in a fluidized-bed reactor, in which case di-tert-butoxy-diacetoxysilane is used as the precursor compound in addition to iron pentacarbonyl. Finally, from WO 2013 / 175339, a purely wet-chemical process is known for coating metal substrates made of aluminum with iron(III) oxide using iron(III) nitrate. Purely wet-chemical processes are also described in WO 2015 / 014484 and WO 2020 / 038684.

[0023] In a specific embodiment, the metallic effect pigment comprises an optionally passivated metal substrate made of aluminum, which is coated with a dielectric layer of silicon dioxide and a dielectric layer of iron(III) oxide, in that order. Instead of a dielectric layer made of iron(III) oxide, a dielectric layer made of iron(III) oxide and titanium(IV) oxide, i.e. a mixed layer, can also be applied to a dielectric layer made of silicon dioxide. In addition, corresponding dielectric layers with low and high refractive index can also be applied alternately to the metal substrate.

[0024] If necessary, the metal effect pigments can be provided with a surface coating. The surface coating can be made of, but is not limited to, organic polymers, silanes or siloxanes. By applying such a surface coating to at least one dielectric layer (also called surface functionalization), the mechanical and chemical resistance of the metal effect pigments can be further increased. The respective procedures are described in detail, inter alia, in WO 2015 / 044188 and EP 2 318 463.

[0025] According to the present invention, the metallic effect pigments have an average pigment thickness of 20 nm to 2000 nm, preferably 50 nm to 1700 nm, more preferably 200 nm to 1500 nm. In this case, the term "pigment thickness" refers to the thickness of the entire metallic effect pigment, i.e. including the thickness of at least one dielectric layer and the thickness of any surface coating that may be applied thereto.

[0026] The average pigment thickness is determined by measurements based on scanning electron microscope (SEM) images. The procedure is as follows: powdered metallic effect pigments are dispersed in a nitrocellulose-based paint and applied to an aluminum foil. The mixing ratio of powder to paint in the liquid system is 1:10. The thickness of a 1 cm2 coating applied in this way is 2Sections of aluminum foil are cut and cross-sectioned by irradiating them with high-energy Ar ions using a broad-beam ion source. A thin 5 nm carbon layer is sputtered onto the cut cross-section to ensure sufficient electrical conductivity. The cross-sections of the metal effect pigments are then imaged using a scanning electron microscope at magnifications ranging from 10,000x to 30,000x. Pigment thicknesses are determined from at least 500 different metal effect pigments. The average pigment thickness then represents the arithmetic number average of the determined pigment thicknesses.

[0027] The relative standard deviation of the average pigment thickness according to the present invention is at most 40%, preferably at most 20%, 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 determined from at least 500 different metal effect pigments. The relative standard deviation of the average pigment thickness is therefore a measure of the variability in the thickness of the metal effect pigments. The smaller the relative standard deviation, the smaller the variability in the thickness of the metal effect pigments.

[0028] The invention is not further limited as far as the size of the metal effect pigments, i.e. the pigment diameter, is concerned. Typically, metal effect pigments have a pigment diameter d in the range of 3 μm to 100 μm, for example in the range of 5 μm to 50 μm, or in the range of 10 μm to 30 μm. 50 The pigment diameter in this case is the so-called d 50 d 50 is the value at which 50% of the metallic effect pigments in the sample exhibit a value less than the specified value. Again, the sample consists of at least 500 different metallic effect pigments.

[0029] Pigment diameter d 50 is determined by measuring based on laser light diffraction according to DIN ISO 13320:2020-01 using a particle size analyzer commercially available from Sympatec GmbH (Clausthal-Zellerfeld, Germany).

[0030] The aspect ratio of metallic effect pigments is ultimately determined by the average pigment thickness and the pigment diameter d 50The aspect ratio, i.e., the pigment diameter d 50 The ratio of the average pigment thickness to the aspect ratio is preferably at least 3: 1, for example at least 4: 1 or at least 5: 1. A large aspect ratio promotes alignment of the metallic effect pigments upon application of the paint formulation to the surface of a vehicle, which has a particularly advantageous effect on the covering power of the vehicle paint obtained from the paint formulation.

[0031] Due to the above-mentioned specific geometrical properties of the metallic effect pigments, the vehicle paint obtained from the paint formulation has, in addition to a sufficiently high light wave reflectance and a sufficiently high radio wave transmittance, also a sufficiently high lightness and a sufficiently high chroma, and has a sufficiently high lightness flop and at the same time a sufficiently high covering power. As the inventors have surprisingly found, this is in particular due to the small variability in the thickness of the metallic effect pigments contained in the paint formulation, expressed by a relative standard deviation of the average pigment thickness of at most 40%, preferably at most 20%, even more preferably at most 10%.

[0032] Since the at least one dielectric layer can be applied to the metal substrate with a high degree of precision in terms of its thickness, the thickness variation of the metallic effect pigments depends primarily on the thickness variation of the metal substrate used for their production. Metal substrates with low thickness variation result in metallic effect pigments with low thickness variation after the application of the at least one dielectric layer. This also applies when a separate surface coating is applied to the at least one dielectric layer. Conversely, metal substrates with high thickness variation result in metallic effect pigments with high thickness variation. The thickness difference of the metal substrate is reflected to some extent in the at least one dielectric layer applied thereto and, optionally, in the surface coating applied thereto.

[0033] Therefore, in order to meet a relative standard deviation of the average pigment thickness of at most 40%, preferably at most 20%, more preferably at most 10%, it is necessary to use metal substrates in the production of metallic effect pigments that have as little thickness variation as possible.

[0034] Metal substrates with the smallest possible thickness variation can be obtained, for example, by vacuum metallization. Vacuum metallization is a specialized form of physical vapor deposition (PVD). For this purpose, a metal such as aluminum is deposited on a carrier film under high vacuum, producing a thin metal layer with a thickness in the nanometer range on the carrier film. The metal layer is then removed from the carrier film using a solvent and crushed into platelets by the shear forces that occur. To facilitate release, a release coating can be applied to the carrier film before deposition. Metal substrates obtained by vacuum metallization are characterized by particularly small thicknesses. Therefore, their thickness variation is also particularly small, so that the metal effect pigments produced therefrom satisfy a relative standard deviation of the average pigment thickness of at most 40%, preferably at most 20%, and more preferably at most 10%.

[0035] In contrast, metal substrates obtained by wet grinding have significantly greater variations in thickness, resulting in a significantly greater relative standard deviation of the average pigment thickness. Metal substrates obtained by wet grinding are also called "cornflakes" or "silver dollars" depending on their appearance. Cornflake-type metal substrates, also called lamellar-type, have irregular, jagged side edges, while lenticular-type "silver dollar" metal substrates typically have rounded edges. Vacuum metallization-derived metal substrates, also called "vacuum metallization pigments," abbreviated VMP, have polygonal shapes with straight side edges. In addition to having particularly small variations in thickness, they also have significantly smoother surfaces than cornflake-type and silver dollar-type metal substrates. In a preferred embodiment, the metal substrate is a vacuum metallization-derived metal substrate.

[0036] The paint formulations used according to the present invention for painting vehicles equipped with radar and lidar sensors may contain a mixture of two or more metal effect pigments. When metal effect pigments are mentioned in this context, those with the specific geometric characteristics described above, particularly those with a small thickness variation, are intended. By using a mixture of two or more metal effect pigments, it is also possible to achieve hues that cannot be easily obtained using a single metal effect pigment. For this purpose, the paint formulation may contain at least one other pigment in addition to the metal effect pigment, including mica- or glass-based pearlescent pigments. However, the pigments contained in the paint formulation can also be limited to metal effect pigments, i.e., the paint formulation does not contain any other pigments in addition to the metal effect pigments. In particular, the paint formulation preferably does not contain, or at most only contains a small proportion of, organic or inorganic absorbing pigments, such as carbon black. As already mentioned at the beginning, the addition of carbon black is accompanied by a loss of brightness. Light wave reflectance also decreases, which adversely affects the measurement accuracy of the lidar sensor. Due to its sufficiently high covering power, the addition of carbon black and the like to the paint formulations used in accordance with the present invention is not required, or is only required to a maximum extent, as will be discussed in more detail below.

[0037] Apart from the pigment, the paint formulation contains a binder and a solvent, and other components such as fillers and / or auxiliaries may also be included in the paint formulation. Typical binders and solvents, as well as all kinds of fillers and auxiliaries, are known to those skilled in the art. Platelets made from calcium carbonate (CaCO3) are mentioned here as an exemplary filler. Examples of auxiliaries include antifoaming agents, wetting agents, light stabilizers, and leveling agents.

[0038] After the paint formulation is applied to the vehicle surface, the solvent is evaporated, and the vehicle coating is finally produced from the paint formulation. The application of the paint formulation is not limited to a specific method. This is conveniently performed by spraying or spraying with a pressure sprayer, and the layer thickness of the vehicle coating obtained from the paint formulation can be adjusted by the application time. Because the paint formulation provides sufficiently high covering power, a relatively small layer thickness is sufficient for vehicle coating. Typical layer thicknesses range from 10 μm to 30 μm, but smaller layer thicknesses are also possible as long as the covering power is sufficiently high. A layer thickness of 14 μm is given here as an example. The layer thickness here always refers to the layer thickness of the vehicle coating, which is reduced compared to the layer thickness of the paint formulation due to the drying of the solvent contained in the paint formulation and, optionally, film formation.

[0039] The pigment mass concentration of metal effect pigments in paint formulations is typically, but not exclusively, in the range of 1% to 15% by mass. Pigment mass concentration means the mass fraction of metal effect pigments relative to the total dry mass of the paint formulation. The total dry mass includes the mass of metal effect pigments as well as the mass of all other non-volatile components. The following applies: the higher the pigment mass concentration, the higher the covering power of the same layer thickness of vehicle paint.

[0040] The paint formulations used according to the present invention for painting vehicles equipped with radar and lidar sensors have sufficiently high covering power. Typically, when the layer thickness of the vehicle paint obtained from the paint formulation is 14 μm and the pigment mass concentration of the metallic effect pigments in the paint formulation is in the range of 1% by weight to 15% by weight, the color distance ΔE110° is at most 1.5, preferably at most 1.2, and more preferably at most 1.0. The color distance ΔE110° is a measure of covering power, with a smaller color distance indicating higher covering power. In this case, a paint with a color distance ΔE110° of at most 1.5 is described as opaque.

[0041] To determine the covering power, the paint formulation is applied to a black and white panel so that the vehicle paint obtained from the paint formulation has a layer thickness of 14 μm.The color distance between black and white is then measured using a commercially available multi-angle spectrophotometer in accordance with DIN 6175:2019-07 in the 45° / 110° configuration.

[0042] The hue of the vehicle paint obtained from a paint formulation depends mainly on the color properties of the metallic effect pigments contained in the paint formulation, but can also be influenced by the addition of other pigments such as mica or glass-based pearlescent pigments, and organic or inorganic absorption pigments. This also applies to lightness and chroma, as well as lightness flop. Hue H, also called hue angle uv An exemplary value of 15° is in the range of 25 to 50, which is typical for red, orange, or gold tones. However, the hue is not limited to this in any way. Therefore, the hue angle may be outside the range of 25 to 50. As far as lightness and chroma are concerned, lightness L * 15° is usually at least 100, and chroma C uv 15° is typically at least 150. The lightness flop, expressed as the Alman flop index FI, is typically at least 20.

[0043] To determine hue, value, saturation, and value flop, the paint formulation is applied to a black background. The spectral reflectance of light incident on the measurement surface at a 45° angle and emitted by a D65 light source is then measured at six different detection angles (-15°, 15°, 25°, 45°, 75°, and 110°) relative to a 10° observer using a commercially available multi-angle spectrophotometer in accordance with DIN EN ISO 18314-3:2018-12. The measured values ​​are then converted to the corresponding variables in the CIELAB and CIE HLC color spaces. The commercially available multi-angle spectrophotometer used here is a "BYK-mac i MetallicColour" device from BYK-Gardner GmbH (Geretsried, Germany), which is also used to determine the color distance ΔE110°. The Armand Flop Index FI is calculated according to ABJ Rodrigues, "Metallic flop and its measurement", J. Oil Color Chem. Assoc. 1992, 75(4), 150-153.

[0044] The paint formulations used in accordance with the present invention for painting vehicles equipped with radar and lidar sensors have sufficiently high light wave reflectivity and sufficiently high radio wave transmittance. In this case, the dielectric constant, also referred to 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 permittivity ε, the less radio wave attenuation occurs. Typically, vehicle paints obtained from the paint formulations have a permittivity ε of at most 30, preferably at most 20, and more preferably at most 10 in the frequency range of 76 GHz to 81 GHz. With such permittivity, the paint formulations are particularly suitable for use in painting vehicles equipped with radar sensors. Additionally, vehicle paints obtained from the paint formulations typically have a reflectivity R of at least 50%, preferably at least 60%, and more preferably at least 70% at a wavelength of 905 nm. With such reflectance, the paint formulation is particularly suitable for use in painting vehicles equipped with lidar sensors.

[0045] The permittivity ε in the frequency range from 76 GHz to 81 GHz is determined using a commercially available radome scanner. After calibration, measurements are taken before and after application of the paint formulation using a 2 mm thick polycarbonate measurement plate. In both cases, a radio beam is irradiated perpendicularly to the surface of the measurement plate. The permittivity ε can finally be determined from the measurements and is constant in this case over the selected frequency range. The commercially available radome scanner used here is the "Radome Measurement System" from perisens GmbH (Feldkirchen, near Munich, Germany). The reflectivity R is similarly determined at a wavelength of 905 nm by irradiating the measurement surface with a light wave perpendicularly.

[0046] The paint formulations can be advantageously used to paint automobiles, especially self-propelled automobiles, equipped with radar and lidar sensors, although in principle any vehicle can be painted with the paint formulations used according to the invention.

[0047] The paint formulation used according to the present invention allows for the cost-effective painting of vehicles equipped with radar and lidar sensors, and the vehicle paint obtained from this paint formulation not only has a sufficiently high light wave reflectance and a sufficiently high radio wave transmittance, but also is characterized by a sufficiently high lightness and a sufficiently high saturation, and has a sufficiently high lightness flop and at the same time a sufficiently high covering power. Thus, the paint formulation used according to the present invention meets the requirements of a paint formulation for use in painting vehicles equipped with radar and lidar sensors without adversely affecting the color properties and covering power. DETAILED DESCRIPTION OF THE INVENTION [Example]

[0048] The following examples serve to further illustrate the present invention without, however, limiting it.

[0049] Paint formulations were prepared using the metallic effect pigments listed in Table 1 (designated pigments a through e, all commercially available).

[0050] Pigments a and b are from Schlenk Metallic Pigments GmbH (Roth, Germany), while pigments c, d, and e are from BASF Colors & Effects GmbH (Ludwigshafen, Germany). The metallic effect pigments are listed in Table 1 together with the average pigment thickness and the absolute standard deviation of the average pigment thickness determined according to the measurement method described above, as well as the resulting relative standard deviation of the average pigment thickness. All metallic effect pigments in Table 1 comprise a metal substrate made from aluminum. In the case of pigments a and b, the aluminum metal substrate is obtained by vacuum metallization, while in the case of pigments c, d, and e, it is obtained by wet milling. In pigments c and d, the aluminum metal substrate is of the "cornflake" type, and in pigment e, it is of the "silver dollar" type.

[0051] [Table 1]

[0052] To prepare the paint formulations, the metallic effect pigments of Table 1 were dispersed in a paint system (a one-component paint based on cellulose acetobutyrate, containing a solvent). In each paint formulation, the metallic interference pigments used were present individually as pure hues or as mixtures, optionally with carbon black paste (Helio Beit® UN 907 from Helio Beit Pigmentpasten GmbH, Cologne, Germany) and / or red pigment paste (Hostatint® Red A-P2Y 100-ST from Clariant AG, Muttenz, Switzerland) as further pigment(s).

[0053] After preparing the coating formulation, it was sprayed onto a polycarbonate measuring plate, resulting in a coating layer 14 μm thick after the solvent evaporated. This coating was then investigated in more detail with regard to its radio wave transmittance and optical wave reflectance, as well as its color properties and covering power. The corresponding parameters were determined according to the measurement methods described above.

[0054] Examples 1 to 4: Hue angle range H uv Paint with an orange tint of 33-35° Table 2 shows the pigment mass concentration PMK of the metallic effect pigments used for each coating. Pigment plus the pigment mass concentration PMK of further pigments, if present w.Pigment In addition, Table 2 shows the dielectric constant ε in the frequency range of 76 GHz to 81 GHz, the reflectance R at a wavelength of 905 nm, and the hue H uv 15°, brightness L * 15°, saturation C uv 15°, the Armand-Flop index FI and the determined color distance ΔE of 110°.

[0055] [Table 2]

[0056] Hue angle H in the range of 33-35, corresponding to an orange hue uv The 15° was almost entirely due to the metallic effect pigments used.

[0057] In Example 1 using pigment a, 12% by weight of PMK was used to achieve an opaque state at a layer thickness of 14 μm. Pigment A pigment mass concentration of 1000 mg / L was required.

[0058] In Example 2, with pigment c (not according to the invention), the pigment mass concentration PMK Pigment The total mass of the fluorine-containing compound was 12% by mass. However, the opaque state was not achieved. The Armand-Flop index (FI) also decreased.

[0059] In Example 3, which used pigment c (not according to the invention), the pigment mass concentration PMK Pigment was increased to 13.42 wt % for the same layer thickness, thus achieving an opaque state. However, this also increased the dielectric constant ε to values ​​above 30 in the frequency range of 76 GHz to 81 GHz.

[0060] In contrast, in Example 4, which used pigment c (not according to the invention), carbon black paste was added to achieve opacity. However, as can be seen from a comparison with Example 1, this was at the expense of color properties. As a result, the reflectance R at a wavelength of 905 nm fell to a value below 50%.

[0061] Based on Examples 1 to 4, it can be concluded that only with a paint formulation containing pigment a can vehicle coatings be obtained which, in addition to a sufficiently high light wave reflectance and a sufficiently high radio wave transmittance, are also characterized by a sufficiently high brightness and a sufficiently high saturation, and which have a sufficiently high brightness flop and at the same time a sufficiently high covering power.

[0062] Examples 5 to 8: Hue angle range H uv Paint with an orange tint of 33-35° Table 3 shows the pigment mass concentration PMK of the metallic effect pigments used for each coating. Pigment plus the pigment mass concentration PMK of further pigments, if present w.Pigment In addition, for each coating, Table 3 lists the dielectric constant ε in the frequency range of 76 GHz to 81 GHz, the reflectance R at a wavelength of 905 nm, and the hue H uv 15°, brightness L * 15°, saturation C uv 15°, the Armand-Flop index FI and the determined color distance ΔE of 110°.

[0063] [Table 3]

[0064] Hue angle H in the range of 33-35, corresponding to an orange hue uv The 15° was almost entirely due to the metallic effect pigments used.

[0065] In Example 5, using pigment a, 12% by weight of PMK was used to achieve an opaque state at a layer thickness of 14 μm. PigmentExample 5 is the same as Example 1.

[0066] In Example 6, with pigment e (not according to the invention), the pigment mass concentration PMK Pigment The total mass of the fluorine-containing compound was 12% by mass. However, the opaque state was not achieved. The Armand-Flop index (FI) also decreased.

[0067] In Example 7, which used pigment e (not according to the invention), the pigment mass concentration PMK Pigment was increased to 19.03 wt % for the same layer thickness, thus achieving an opaque state. However, this also increased the dielectric constant ε to values ​​above 30 in the frequency range of 76 GHz to 81 GHz.

[0068] In contrast, in Example 8, which used pigment e (not according to the invention), carbon black paste was added to achieve opacity. However, as can be seen from a comparison with Example 5, this was at the expense of color properties. As a result, the reflectance R at a wavelength of 905 nm was reduced to a value below 50%.

[0069] Based on Examples 5 to 8, it can be concluded that only with a paint formulation containing pigment a can vehicle coatings be obtained which, in addition to a sufficiently high light wave reflectance and a sufficiently high radio wave transmittance, are also characterized by a sufficiently high brightness and a sufficiently high saturation, and which have a sufficiently high brightness flop and at the same time a sufficiently high covering power.

[0070] Examples 9 to 12: Hue angle range H uv 15° paint with a gold hue of 47-48 Table 4 shows the pigment mass concentration PMK of the metallic effect pigments used for each coating. Pigment plus the pigment mass concentration PMK of further pigments, if present w.Pigment In addition, for each coating, Table 4 shows the dielectric constant ε and hue H in the frequency range of 76 GHz to 81 GHz. uv 15°, brightness L* 15°, saturation C uv 15°, the Armand-Flop index FI and the determined color distance ΔE of 110°.

[0071] [Table 4]

[0072] Hue angle H in the range of 47-48, which corresponds to a golden hue uv The 15° was almost entirely due to the metallic effect pigments used.

[0073] In Example 9, using pigments a and b, 6.865% by weight of PMK was used to achieve an opaque state at a layer thickness of 14 μm. Pigment A pigment mass concentration of Pigment A and Pigment B was required. Pigment A and Pigment B were present in a 50:50 mass ratio.

[0074] In Example 10, with pigment d (not according to the invention), the pigment mass concentration PMK Pigment The chromaticity was 6.865% by mass. However, the opaque state was not achieved. The Armand-Flop index (FI) also decreased.

[0075] In Example 11, with pigment d (not according to the invention), the pigment mass concentration PMK Pigment was increased to 11.637 wt % for the same layer thickness, thus achieving an opaque state. However, this also increased the dielectric constant ε to values ​​above 30 in the frequency range of 76 GHz to 81 GHz.

[0076] In contrast, in Example 12, which used pigment d (not according to the invention), carbon black paste was added to achieve opacity, but this was at the expense of color properties, as can be seen from a comparison with Example 9.

[0077] Based on Examples 9 to 12, it can be concluded that only with a paint formulation containing pigment a and pigment b can vehicle coatings be obtained which, in addition to a sufficiently high light wave reflectance and a sufficiently high radio wave transmittance, are also characterized by a sufficiently high brightness and a sufficiently high saturation, and which have a sufficiently high brightness flop and at the same time a sufficiently high covering power.

[0078] Examples 13 to 16: Hue angle range H uv 15° paint with a red tint of 27-28 Table 5 shows the pigment mass concentration PMK of the metallic effect pigments used for each coating. Pigment plus the pigment mass concentration PMK of the further pigment(s), if present w.Pigment In addition, for each coating, Table 5 lists the dielectric constant ε in the frequency range of 76 GHz to 81 GHz, the reflectance R at a wavelength of 905 nm, and the hue H uv 15°, brightness L * 15°, saturation C uv 15°, the Armand-Flop index FI and the determined color distance ΔE of 110°.

[0079] [Table 5]

[0080] Hue angle H in the range of 27-28, corresponding to red hues uv The 15° resulted from the combination of metallic effect pigments and red pigment paste used.

[0081] In Example 13 using pigment a, 12.052% by weight of PMK was used to achieve an opaque state at a layer thickness of 14 μm. Pigment A pigment mass concentration of 1000 mg / L was required.

[0082] In Example 14, pigment a was used, and the pigment mass concentration PMK was PigmentThe reflectance R at a wavelength of 905 nm also decreased to a value below 50%. To achieve opacity, carbon black paste was added. However, as can be seen from a comparison with Example 13, this was at the expense of color properties. As a result, the reflectance R at a wavelength of 905 nm also decreased to a value below 50%.

[0083] In Example 15, which used pigment e (not according to the invention), and in Example 16, which used pigment c (not according to the invention), it was necessary to add much more carbon black paste at the same layer thickness to achieve an opaque state. However, as can be seen from a comparison with Example 13, this was at the expense of color properties. As a result, the reflectance R at a wavelength of 905 nm also decreased to a value below 50%.

[0084] Based on Examples 13 to 16, it can be concluded that only with a paint formulation containing pigment a can vehicle coatings be obtained which, in addition to a sufficiently high light wave reflectance and a sufficiently high radio wave transmittance, are also characterized by a sufficiently high brightness and a sufficiently high saturation, and which have a sufficiently high brightness flop and at the same time a sufficiently high covering power.

Claims

1. 1. A paint formulation containing metallic effect pigments for painting vehicles equipped with radar and lidar sensors, said metallic effect pigments comprising a metal substrate, optionally passivated and coated with at least one dielectric layer, said metallic effect pigments having an average pigment thickness of 20 nm to 2000 nm, the relative standard deviation of said average pigment thickness being at most 40%.

2. 10. The coating formulation of claim 1, wherein the metal substrate is made from aluminum.

3. 3. A coating formulation according to claim 1 or 2, wherein the at least one dielectric layer is of a dielectric selected from silicon dioxide, aluminium oxide, iron (III) oxide, titanium (IV) oxide, tin (IV) oxide, chromium (III) oxide and cobalt (III) oxide.

4. A paint formulation according to any one of claims 1 to 3, wherein said metallic effect pigment is an interference pigment.

5. A paint formulation according to any one of claims 1 to 4, wherein the metallic effect pigments are provided with a surface coating.

6. A paint formulation according to any one of claims 1 to 5, wherein the relative standard deviation of the average pigment thickness is at most 10%.

7. The metallic effect pigments have a pigment diameter d in the range of 3 μm to 100 μm ５０ 7. The paint formulation according to any one of claims 1 to 6, having

8. A coating formulation according to any one of claims 1 to 7, wherein the metal substrate is a metal substrate obtained by vacuum metallization.

9. A paint formulation according to any one of the preceding claims, wherein the paint formulation contains a mixture of two or more of said metallic effect pigments.

10. A paint formulation according to any one of the preceding claims, wherein the paint formulation contains at least one further pigment in addition to the metallic effect pigment.

11. A paint formulation according to any one of claims 1 to 10, wherein the paint formulation does not contain any carbon black.

12. 12. The paint formulation according to any one of the preceding claims, wherein the color distance ΔE110° is at most 1.5 when the layer thickness of the vehicle paint obtained from said paint formulation is 14 μm and the pigment mass concentration of said metallic effect pigments in the paint formulation is in the range of 1% by weight to 15% by weight.

13. The vehicle paint obtained from said paint formulation has a hue H in the range of 25 to 50. ｕｖ 15°, lightness L of at least 100 ＊ 15°, chroma C of at least 150 ｕｖ 13. The paint formulation of claim 12 having a curvature of 15° and an Armand-Flop index FI of at least 20.

14. 14. The paint formulation according to claim 12 or 13, wherein the vehicle paint obtained from said paint formulation has a dielectric constant ε of at most 30 in the frequency range of 76 GHz to 81 GHz and a reflectance R of at least 50% at a wavelength of 905 nm.

15. A paint formulation according to any one of claims 1 to 14, wherein the vehicle is an automobile.

16. The paint formulation of claim 15, wherein the motor vehicle is a self-propelled motor vehicle.

Images