LiDAR REFLECTIVE COATING

Abstract

The present invention relates to a pigmented paint composition comprising (A) at least one film-forming polymer (A1) and, if (A1) is externally crosslinkable, at least one crosslinking agent (A2); (B) at least two types of metallic effect pigments (B); (C) at least one type of LiDAR reflective mica pigment (C); and (D) water and / or one or more organic solvents as component (D). The invention further relates to a method of forming a coating layer or a multilayer coating and to a method of improving the LiDAR reflectance and / or LiDAR detectability of an object. Furthermore, the invention relates to a coating layer formed using the colored paint composition according to the invention and to a coated substrate. The invention also relates to the use of the coated substrate in LiDAR visibility applications involving vehicles and parts thereof.

Description

[0001] The present invention relates to a light silver paint composition comprising a metallic effect pigment, a mica pigment and optionally a blend of near-infrared reflecting and / or near-infrared transparent color pigments. The present invention further relates to a method of forming a coated film using the paint composition, a coated film thus obtained and a substrate at least partially coated therewith, and to the use of the coating in LiDAR applications. Background Art

[0002] Recently, progress has been made in technologies related to autonomous vehicles and vehicles with ADAS (Advanced Driver Assistance Systems). Vehicles with ADAS reduce driving stress, reduce the number of accidents, improve fuel economy, etc.

[0003] Typically, such technologies require detecting objects around the vehicle. Detection systems generally include sensors, cameras, radars, ultrasounds and lasers to detect and locate obstacles so that the vehicle can safely bypass such objects. Some detection systems are limited in their ability to detect objects at long distances or in non-ideal environments such as in low light conditions, in adverse weather such as fog, rain and snow, or in other conditions where there are light scattering particles in the air (e.g., haze and dust). Such limitations may prevent the vehicle from safely bypassing obstacles.

[0004] ADAS highly relies on remote sensing technologies by optical or electromagnetic means for determining position and speed.

[0005] LiDAR ( Optical probe Light Detection and Ranging) is a remote sensing technology that can be deployed as a primary source of object recognition in such vehicles. By irradiating the surrounding environment with a laser (typically 905 nm or 1550 nm), LiDAR maps the distances to the objects in its path in real time and can be paired with software to safely react to the objects in its vicinity. For example, if an object is too close to the vehicle, the software can react to avoid a collision with the object. Since LiDAR uses near-infrared light (near-IR light or NIR light) as its illumination source, this technology must overcome several challenges.

[0006] Although many light-colored objects reflect this type of light well over a wide range of incident angles, silver coatings, especially those containing aluminum flake pigments, need improvement at higher incident angles.

[0007] This shows that in addition to the LiDAR instrument, one of the important factors for measurement accuracy is also the surface of the object being irradiated. In the case of automobiles and other vehicles, the surface is usually covered with multiple layers of coatings, which play an important role in determining the LiDAR reflectivity.

[0008] The ability of an object to reflect light depends on its volume and surface properties and manifests itself as specular or diffuse reflection. Specular reflection of light occurs when incident light from a single direction of a light source is reflected as an incident wave in a single outgoing direction at an angle opposite to the plane normal to the reflecting surface. Diffuse reflection occurs when incident light from a single direction of a light source is reflected at multiple angles. In theory, both specular and diffuse reflection can be used in a vehicle's LiDAR technology, but in practice, this is much more difficult. Regarding specular reflection, most of the brightness is observed at an angle opposite to the angle of incidence. Thus, for a moving vehicle with a detector located at the light source, this can be a problem if the angle of incidence is far from the alignment of the series light source and detector. Although typically at low angles of incidence, such as from 0° to 10°, the LiDAR reflectivity is at its maximum, the LiDAR reflectivity significantly decreases at higher angles of incidence, such as at an angle of incidence of 15° or more with respect to the plane normal to the reflecting surface. Thus, the object of the present invention is to significantly improve the LiDAR reflectivity at angles of incidence of 15° and higher, particularly in the range from about 15° to about 40°, which is crucial in many automotive applications.

[0009] Nevertheless, most existing coatings are applied to substrates such as vehicle bodies to improve durability and aesthetics but generally do not confer sufficient functionality in reflecting near-IR light to enhance the visibility of LiDAR technology.

[0010] In recent years, several methods have been developed to improve the LiDAR reflectivity of multi-layer coatings, particularly those applied to vehicles. To understand these methods, the typical structure of automotive multi-layer coatings needs to be considered. The coating layers on a vehicle body and its parts typically start from the substrate with a conversion coating layer, an electrodeposition coating layer (such as preferably a cathodic electrodeposition layer), a primer layer (also called a filler layer), a basecoat layer, and a clearcoat layer as a topcoat on top of the basecoat layer. The above-mentioned primer layer, basecoat layer, and clearcoat layer are generally referred to as the three-coat system.

[0011] In a first method, the basecoat layer contains NIR-reflective pigments. The NIR light passes through the non-NIR-absorbing protective clearcoat layer and is reflected by one or more NIR-reflective pigments in the basecoat layer. In a different second method, the NIR light passes through the non-NIR-absorbing protective clearcoat layer and the basecoat layer that may contain non-NIR-absorbing colored pigments but is reflected by the underlying primer layer or the substrate (if no primer layer is present).

[0012] Although both methods are effective for solid-color multi-layer coatings, problems arise when the color paint layer contains metallic effect pigments to provide a multi-layer coating with a so-called brightness angle-dependent color effect, particularly if the brightness angle-dependent color effect is provided in the form of a silver-metallic multi-layer coating. The term "brightness angle-dependent color effect" (or simply angle-dependent color effect as used herein) refers to the difference in the amount or hue of light reflected from the surface of a metallic coating at different angles. The angle-dependent color effect depends on the particle size and distribution, particle shape, and orientation of the effect pigment particles in the coating layer. The degree of the angle-dependent color effect can be represented by a so-called angle-dependent color index, which is a measure of the change in reflectance as a metallic coating containing flaky pigments is rotated over the entire viewing angle range. An angle-dependent color index of 0 indicates a solid color, while a very high angle-dependent color effect may even result in an angle-dependent color index higher than 15.

[0013] Generally, larger flaky particles are better reflectors, which results in a higher angle-dependent color index and brightness, while smaller particles exhibit less angle-dependent color because the amount of light scattered at the edges increases with non-directional reflection. In the case of even coarser metallic pigments, individual particles become more apparent, resulting in a grainy or textured appearance.

[0014] Thus, although the most desirable flaky metallic pigments are typically highly reflective and coatings obtained by using such pigments typically have a high angle-dependent color index, they also have a very high specular reflectivity and thus a low reflectivity in the range of angles deviating from the specular reflection angle, which adversely affects the LiDAR reflectivity of those vehicles that are not directly in front of the light source / detector system but at an angle to it or in its adjacent lanes.

[0015] As a result, coatings obtained by using conventional metal-containing pigment coating compositions exhibit a rather high angle-dependent color index of 9 and above, while their LiDAR reflectivity at an incident angle of 45° is typically even lower than 5%. Generally, the higher the angle-dependent color effect, the lower the LiDAR reflectivity.

[0016] Therefore, an object of the present invention is to maintain the brightness angle-dependent color effect at approximately the same level as that of a conventional silver-metallic coating, while improving the visibility of such coated objects to LiDAR detection, particularly for light-colored coatings. This should be achieved by providing a color paint composition that contains flaky metallic pigments to achieve a high angle-dependent color index for the coatings obtained therewith and should further contain components that have no or only a small effect on the angle-dependent color index but tend to significantly increase the LiDAR reflectivity of the coating layer formed by the coating composition. In addition, the components to be added to a conventional silver-metallic color paint composition should have a relatively low hiding power so that the multi-layer coating including such a color paint layer has an excellent appearance, which appearance includes the color effect provided by the primer layer of such a multi-layer coating. SUMMARY OF THE INVENTION

[0017] The above object is achieved by providing a colored paint composition comprising:

[0018] (A) At least one film-forming polymer (A1), and when (A1) is externally crosslinkable, at least one crosslinking agent (A2);

[0019] (B) At least two types of metallic effect pigments (B); and

[0020] (C) At least one type of LiDAR reflective mica pigment (C),

[0021] (D) Water and / or one or more organic solvents as component (D).

[0022] For the sake of facilitating the understanding of LiDAR reflection, the angle of incidence, and other terms used herein, reference is made to Figure 1 , where 1 and Θ I represent the emitter and the angle of incidence, 2 and Θ R represent specular reflection and the reflection angle, and 3 represents the receiver (opposite angle).

[0023] Another object of the present invention is a method for at least partially forming a coating layer on at least one surface of a substrate, wherein the method at least comprises step (a), that is

[0024] (a) Applying at least partially the colored paint composition according to the present invention to at least one surface of an optionally pre-coated substrate to form a coating layer on the surface of the substrate.

[0025] This method, after the following steps:

[0026] (b) Curing the paint layer obtained after performing step (a) to form a cured coating on the surface of the substrate,

[0027] is also a suitable method for improving the LiDAR reflectivity and / or LiDAR detectability of an object, wherein the substrate is the object or becomes part of the object, which will be improved in terms of LiDAR reflectivity and / or LiDAR detectability.

[0028] A method for forming a multi-layer coating including the above method for forming a coating layer and a method for improving the LiDAR reflectivity and / or LiDAR detectability of an object by using the method for forming a multi-layer coating are also objects of the present invention.

[0029] Yet another object of the present invention is a coating layer obtainable from the coating composition according to the present invention or by the method according to the present invention.

[0030] A further object of the present invention is at least partially coated substrates obtainable by the method according to the present invention.

[0031] Another object of the present invention is the use of the coating composition of the present invention in LiDAR visibility applications, especially for autonomous driving systems such as autonomous vehicles and vehicles with ADAS. Detailed Description

[0032] Color paint composition

[0033] The color paint composition of the present invention (also referred to herein as the coating composition of the present invention) can be a solvent-based color paint composition (hereinafter also referred to as a solvent-based color paint composition) or an aqueous color paint composition (hereinafter also referred to as an aqueous-based color paint composition). Preferably, the coating composition is an aqueous color paint composition. Preferably, the coating composition is used as a one-pack solvent-based or water-based color paint composition. The coating composition of the present invention is particularly not a primer, a primer surfacer or a sealant composition and thus is not used / applied as a primer, a primer surfacer or a sealant composition. It typically forms a color paint layer in direct contact with one or more clearcoat layers of a multi-layer coating.

[0034] The coating composition according to the present invention is suitable for producing a color paint layer. Thus, the coating composition according to the present invention is especially a solvent-based color paint composition or an aqueous color paint composition.

[0035] The term "color paint" is known in the art and is defined, for example, in Lexikon, "Lacke und Druckfarben" ("Paints and Printing Inks"), Georg Thieme Verlag, 1998, 10th edition, page 57. Thus, color paints are especially used for automotive coatings and general industrial paint coloring in order to give a coloring and / or optical effect by using the color paint as an intermediate coating composition. Color paint compositions are usually applied to metal or plastic substrates (optionally pretreated and / or pre-coated with a primer and / or filler), and sometimes in the case of plastic substrates, it can also be applied directly onto the plastic substrate, and in the case of metal substrates, it is applied onto an electrodeposition coating applied to the metal substrate or onto a metal substrate already provided with a primer and / or filler and / or electrodeposition coating, or in the case of a refinish paint application, it is applied onto an existing coating, which existing coating can also serve as a substrate. In order to protect the color paint layer especially from environmental influences, at least one additional clearcoat layer is applied thereto.

[0036] In the general context of the present invention and in particular in relation to the coating composition according to the present invention, the term "comprising" has the meaning of "containing" rather than "consisting of". In particular, "comprising" means that in addition to components (A1), (A2), (B), (C) and (D), one or more of the other components mentioned below may also optionally be included in the coating composition according to the present invention. According to the preferred embodiments mentioned hereinafter, all components may be present in each case.

[0037] The proportions and amounts, in wt.-% (i.e., % by weight), of all components (A1), (A2), (B), (C) and (D) in the coating composition according to the present invention and of the optionally additionally present components together amount to 100 wt.-% based on the total weight of the coating composition.

[0038] As used herein, the term "near-IR" or "near-infrared radiation or light" or "NIR" refers to electromagnetic radiation in the near-infrared range of the electromagnetic spectrum. Such near-IR electromagnetic radiation may have a wavelength of 800 nm to 2500 nm, such as 850 to 2000 nm or such as 900 nm to 1600 nm. In particular, the NIR light used has a wavelength of 880 nm to 930 nm, with 905 nm as the central wavelength. Sources of near-IR electromagnetic radiation that can be used in the present invention to generate NIR light include, but are not limited to, light-emitting diodes (LEDs), laser diodes or any light source that can emit electromagnetic radiation having a wavelength in the range of 800 nm to 2500 nm (in the near-IR range). Sources of near-IR electromagnetic radiation can be used in LiDAR (light detection and ranging) systems. LiDAR systems can utilize lasers to generate electromagnetic radiation having a wavelength of 900 nm to 1600 nm.

[0039] Preferably, the coating layer obtained from the coating composition according to the present invention is capable of reflecting NIR light, preferably NIR light having a wavelength of 800 to 2500 nm.

[0040] In addition to the pigments of components (B) and (C), the paint composition according to the present invention may also contain one or more additional pigments as component (E).

[0041] If additional pigments (E) are included, they should preferably be LiDAR-reflective or LiDAR-transparent, i.e., preferably not LiDAR-absorbing.

[0042] Preferably, the coating composition of the present invention does not contain any additional components as fillers. Therefore, the coating composition of the present invention preferably does not contain fillers. If any components (i.e., pigments and / or fillers other than (B), (C), and (E)) are included in the coating composition, these components preferably do not absorb or preferably substantially do not absorb light. Herein, a thickener (i.e., a thickening agent) is not considered to be included in the term "pigment and / or filler".

[0043] Preferably, the solids content of the coating composition according to the present invention is in the range of 10 wt.-% to 35 wt.-%, more preferably 15 wt.-% to 30 wt.-%, even more preferably 17 wt.-% to 28 wt.-%, most preferably 19 wt.-% to 26 wt.-%, especially 20 wt.% to 24 wt.%. The determination of the solids content (i.e., the non-volatile content) is carried out by drying a 1 g sample of the coating composition at 125 °C for 60 min. The details of this method are disclosed in the experimental part of the present invention.

[0044] Film-forming polymer (A1)

[0045] The coating composition of the present invention contains at least one film-forming polymer as the film-forming binder (A1) of the coating composition.

[0046] For the purposes of the present invention, the term (A1) should be understood as the non-volatile component of the coating composition that is responsible for film formation and does not include additives, especially does not include additive (E). Preferably, at least one polymer of the at least one polymer (A1) is the main binder of the coating composition. As the main binder in the present invention, when no other binder components are present in the coating composition, the binder component present in a higher proportion based on the total weight of the coating composition is preferably mentioned.

[0047] The term "polymer" is known to those skilled in the art and for the purposes of the present invention encompasses addition polymers and polymerizates as well as condensation polymers. The term "polymer" includes both homopolymers and copolymers.

[0048] The at least one polymer used as component (A1) can be physically drying, self-crosslinkable or externally crosslinkable. Suitable polymers that can be used as component (A1) are described, for example, in EP 0 228 003 A1, DE 44 38 504 A1, EP 0593 454 B1, DE 199 48004A1, EP 0 787 159 B1, DE 40 09 858 A1, DE 44 37 535 A1, WO92 / 15405A1 and WO 2005 / 021168 A1.

[0049] The at least one polymer used as component (A1) is preferably selected from the group consisting of polyurethanes, polyureas, polyesters, polyamides, poly(meth)acrylates and / or copolymers of the structural units of said polymers, in particular polyurethane-poly(meth)acrylates and / or polyurethane polyureas. The at least one polymer used as component (A1) is particularly preferably selected from the group consisting of polyurethanes, polyesters, poly(meth)acrylates and / or copolymers of the structural units of said polymers. In the context of the present invention, the terms “(meth)acryloyl” or “(meth)acrylate” in each case include the meanings “methacrylic” and / or “acrylic” or “methacrylate” and / or “acrylate”.

[0050] Preferred polyurethanes are described, for example, on pages 4, line 19 to page 11, line 29 of German patent application DE 199 48 004 A1 (polyurethane prepolymer B1), on pages 3, line 24 to page 5, line 40 of European patent application EP 0 228 003 A1, on pages 3, line 38 to page 8, line 9 of European patent application EP 0 634 431 A1, and on pages 2, line 35 to page 10, line 32 of international patent application WO92 / 15405.

[0051] Preferred polyesters are described, for example, in columns 6, line 53 to column 7, line 61 and columns 10, line 24 to column 13, line 3 of the described DE 4009858 A1 or on pages 2, line 24 to page 7, line 10 and pages 28, line 13 to page 29, line 13 of WO 2014 / 033135 A2. Similarly, the polyesters can have a dendritic structure, as described, for example, in WO 2008 / 148555 A1.

[0052] Preferred polyurethane-poly(meth)acrylate copolymers (for example, (meth)acrylated polyurethanes) and their preparation are described, for example, on pages 3, line 21 to page 20, line 33 of the described WO 91 / 15528 A1 and on pages 2, line 27 to page 6, line 22 of DE 4437535 A1.

[0053] Preferred poly(meth)acrylates are those which can be prepared by multistage radical emulsion polymerization of ethylenically unsaturated monomers in water and / or organic solvents. For example, seed-core-shell polymers (SCS polymers) are particularly preferred. Such polymers or aqueous dispersions containing such polymers are known, for example, from WO 2016 / 116299 A1.

[0054] Preferred polyurethane-polyurea copolymers are polyurethane-polyurea particles, preferably those having an average particle size of 40 to 2000 nm. These polyurethane-polyurea particles are each in a reacted form and contain at least one isocyanate group-containing polyurethane prepolymer (containing anionic groups and / or groups that can be converted into anionic groups) and at least one polyamine containing two primary amine groups and one or two secondary amine groups. Preferably, such copolymers are used in the form of an aqueous dispersion. Such polymers can in principle be prepared by conventional addition polymerization of, for example, polyisocyanates with polyols and polyamines.

[0055] The polymer used as component (A1) preferably has reactive functional groups that enable a crosslinking reaction. Any common crosslinkable reactive functional groups known to those skilled in the art can be present. Preferably, the polymer used as component (A1) has at least one functional reactive group selected from the group consisting of: primary amine groups, secondary amine groups, hydroxyl groups, thiol groups, carboxyl groups, and urethane groups. Preferably, the polymer used as component (A1) has a hydroxyl functional group.

[0056] Preferably, the polymer used as component (A1) is hydroxyl-functional and more preferably has an OH value in the range of 10 to 500 mg KOH / g, more preferably 40 to 200 mg KOH / g.

[0057] The polymer used as component (A1) is particularly preferably a hydroxyl-functional polyurethane-poly(meth)acrylate copolymer, a hydroxyl-functional polyester, and / or a hydroxyl-functional polyurethane-polyurea copolymer.

[0058] In addition, the coating composition of the present invention can contain at least one typical crosslinking agent known per se. The crosslinking agent is included in the film-forming non-volatile components of the coating composition and thus falls within the general definition of "binder". Therefore, the crosslinking agent is classified under component (A).

[0059] Crosslinking agent (A2)

[0060] If (A1) is externally crosslinkable, a crosslinking agent (A2) is required for crosslinking. The crosslinking agent is preferably at least one aminoplast resin and / or at least one blocked or free, preferably blocked polyisocyanate, and most preferably an aminoplast resin. In the case of an aqueous one-pack paint composition, it is most preferred to have an aminoplast resin. Among these aminoplast resins, melamine resins such as melamine-formaldehyde resins are particularly preferred.

[0061] Metallic effect pigment (B)

[0062] The term "metallic effect pigment" is used according to EN ISO 18451-1:2019 (Pigments, dyestuffs and extenders - Vocabulary - Part 1). Metallic effect pigments are defined as flaky pigments consisting of metals. In the present invention, the term "consisting of metals" does not exclude surface modification of the metallic effect pigments, such as the presence of additional oxide layers, such as a silica layer for example. Similarly, the term "metal" as used in the term "metallic effect pigment" includes metals and metal alloys. Metallic effect pigments - as already listed above - can be oriented parallel and exhibit metallic luster due to light reflection at the flakes.

[0063] Typical metals and alloys used in metallic effect pigments are aluminum and its alloys. Most suitable and preferred in the present invention are flaky aluminum effect pigments, which can be coated or uncoated and are preferably coated, especially in the case of the preferred aluminum pigments, to inhibit their reaction with water in aqueous paint compositions. Such inhibition can be achieved, for example, by stabilizing with organic phosphorus; passivating the aluminum pigments with a conversion layer by chromic acid passivation; encapsulating with a protective layer such as a polymer coating or a silica coating (Peter Wiβling, "Metallic Effect Pigments", Vincentz Network 2006, pages 85 - 89). Such aluminum effect pigments are commercially available, for example, from ECKART GmbH (Germany) under the trade names Hydroxal (stabilized), Hydrolux (chromic acid passivated) and Hydrolan (silica encapsulated). Further modification of the pigment surface is also possible, for example, by modification with non-polar groups such as alkyl groups, thus producing a so-called semi-leafing effect.

[0064] Metallic effect pigments, especially aluminum effect pigments, can be coated with oxide layers such as silica layers and / or chromium(III) oxide layers, which further contribute to stabilizing the pigments against mechanical shock and particularly improve circulation line stability. In the present invention, oxide-encapsulated aluminum metallic effect pigments are preferred. Preferably, based on the sum of the amounts of aluminum and the oxide layer in such preferred aluminum effect pigments, the amount of the oxide layer ranges from 3 wt.-% to 15 wt.-%, more preferably from 5 wt.-% to 12 wt.-% and most preferably from 6 wt.-% to 10 wt.-%. However, the term "metallic effect pigment" encompasses such coated pigments, and the total weight of such coated metallic effect pigments should be understood as the weight of the metallic effect pigment. Thus, the weight includes the coating material.

[0065] In the present invention, at least two types of metallic effect pigments, preferably at least two types of aluminum effect pigments, are used in the paint composition of the present invention.

[0066] As described above, metallic effect pigments are by definition flaky. However, they can have different particle shapes and different particle size distributions, and can be floating or non-floating metallic effect pigments. In the present invention, the at least two different metallic effect pigments are preferably non-floating pigments, more preferably non-floating aluminum effect pigments having different shapes and / or different particle size distributions.

[0067] The shape of the pigment particles used in the present invention varies according to the pigment manufacturing method. These shapes range from irregularly formed flakes (referred to as cornflake pigments) to almost circular flakes with a minimum scattering ratio (referred to as silver dollar pigments). Pictures and typical characteristics of both cornflake pigments and silver dollar pigments are shown, for example, in the textbook by Peter Wiβling, "Metallic Effect Pigments", Vincentz Network 2006, pages 31 - 33. In the present invention, it is preferred that at least one type of metallic effect pigment used in the paint composition of the present invention is a cornflake metallic effect pigment, preferably a cornflake aluminum effect pigment, and at least one different type of metallic effect pigment used in the paint composition of the present invention is a silver dollar metallic effect pigment, preferably a silver dollar aluminum effect pigment. Typically, cornflake aluminum pigments exhibit a higher LiDAR reflectance ratio at an incident angle in the range of 25° to 40°.

[0068] In addition to the pigment shape, the pigment particle size distribution is also a characteristic of the at least two metallic effect pigments to be used in the paint composition of the present invention.

[0069] The particle size distribution is typically represented by volume-based D10, D50, and D90 values determined with a Malvern Zetasizer as detailed in the experimental section of this specification. D10 defines the proportion of particles with a diameter less than this value as 10%. D50 defines the proportion of particles with a diameter less than this value as 50% and is also referred to as the median diameter. D90 defines the proportion of particles with a diameter below this value as 90%.

[0070] Preferably, the two types of metallic effect pigments have a volume-based D90 value of less than 60 μm, more preferably less than 50 μm; a volume-based D50 value of less than 40 μm, more preferably less than 30 μm; and a volume-based D10 value of less than 25 μm, more preferably less than 20 μm. Generally, the higher the D50 value, the higher the loss of the LiDAR reflectance, especially at the incident angles in the range of 25° to 40°.

[0071] The flake thickness of such metallic effect pigments is preferably in the range of 150 to 1000 nm, more preferably 200 to 900 nm, such as 300 to 800 nm, as determined by electron microscopy as described in the experimental part of this specification. Generally, the larger the flake thickness, the lower the LiDAR reflectance.

[0072] Most preferably, at least two different types of metallic effect pigments are used, wherein the first type has a narrow particle size distribution and the second type has a wide particle size distribution. The width or narrowness of the particle size distribution can be determined by calculating the particle size distribution span (PSDS), which is obtained by the following equation: PSDS = [(D90 - D10) / (D50)]. The larger the PSDS, the wider the particle size distribution.

[0073] In the present invention, preferably, the difference between the particle size distribution spans of the metallic effect pigment (B) with the largest PSDS and the metallic effect pigment (B) with the smallest PSDS is in the range of 0.2 to 1.0, even more preferably in the range of 0.3 to 0.9, or most preferably in the range of 0.4 to 0.8.

[0074] It is also possible and preferred that the paint composition contains more than two different types of metallic effect pigments, such as three different types of metallic effect pigments, preferably three types of aluminum effect pigments.

[0075] Preferably, based on the total amount of the metallic effect pigment (B), each of the two or more different metallic effect pigments is present in an amount of at least 5 wt.-%, and the total amount of the metallic effect pigment (B) totals up to 100 wt.-%.

[0076] The total amount of all the metallic effect pigments (B) in the paint composition of the present invention is preferably in the range of 0.2 wt.-% to 8.0 wt.-%, more preferably in the range of 0.5 wt.-% to 5.0 wt.-%, and most preferably in the range of 1.0 wt.-% to 4.0 wt.-% based on the total weight of the coating composition.

[0077] The weight ratio of (B) / [(A1)+(A2)] in the coating composition of the present invention is preferably in the range of 0.01 to 0.40, more preferably in the range of 0.02 to 0.30, even more preferably in the range of 0.04 to 0.20 and most preferably in the range of 0.06 to 0.18, such as 0.08 to 0.15.

[0078] The metallic effect pigments are preferably used in the coating composition of the present invention in the form of a pigment paste, such pigment pastes preferably containing 40 wt.-% to 70 wt.-%, more preferably 50 wt.-% to 65 wt.-% of metallic effect pigments based on the total weight of the paste. The volatile part is typically an organic solvent such as an alcohol, preferably isopropanol. The paste may further contain small amounts of lubricants and other additives.

[0079] Mica pigment (C)

[0080] The platelet mica pigment (C) to be used in the paint composition of the present invention is a LiDAR reflective pigment as known to those skilled in the art. As used herein, the LiDAR reflective mica pigment preferably has a LiDAR reflectance of at least 5% at an angle of incidence of 15°, which LiDAR reflectance is measured by using an overcoated Metopac TM T12G test panel on the black side of the panel.

[0081] As mica pigments, natural mica pigments as well as synthetic mica pigments can be used, provided they are LiDAR reflective.

[0082] As used herein, the term "synthetic mica" represents "fluorinated mica" or "fluorphlogopite", i.e. such mica in which the OH groups are replaced by F groups in the corresponding mica formula.

[0083] Unlike natural mica, which is mined in the presence of sand, kaolin, feldspar and other silicates and may contain impurities such as iron oxide and heavy metals, synthetic mica is free of such impurities. Due to the presence of these additional impurities, natural mica may discolour. In some cases, this discolouration is an undesirable feature of the natural material. However, if used in small amounts, it is acceptable.

[0084] Natural mica has to be ground to produce flakes. This grinding process typically does not allow for tight control of the smoothness, stepped features and flake thinness of the mica surface. As a result, the flakes typically have imperfect edges and faces and less specular reflection (edge scattering).

[0085] Synthetic fluorophlogopite can be synthesized as described, for example, in US2014 / 0251184 A1 or using the Bridgman-Stockbarger method with a platinum crucible and a seed crystal. In particular, fluorophlogopite is a widely used pigment having the formula KMg3AlSi3O 10 F2. This fluorinated mica is one of the most important in the present invention and is commonly used in cosmetic formulations.

[0086] In the present invention, among the fluorinated micas, particularly preferred fluorophlogopite is used, which is preferably covered or coated with titanium dioxide, iron oxide, and / or silane-treated. How to coat synthetic mica with, for example, titanium dioxide is disclosed, for example, in EP 3 719081 A1, but also belongs to the prior art since most mica products on the market are coated with metal oxides of different compositions.

[0087] The synthetic and natural mica pigments (C) used herein preferably contain titanium dioxide as a coating. However, small amounts of other oxides in the coating, such as iron oxide, etc., are also suitable. In addition, some preferred grades may contain silane as a surface modifier, and the amount is preferably 0 to 3 wt.-% based on the total weight of the pigment (C).

[0088] As the mica pigment (C), most preferably, it is a synthetic or natural mica pigment coated and / or surface-treated with one or more titanium oxide minerals. The titanium minerals are preferably selected from the group including: titanium dioxide, such as rutile, anatase, and brookite; and iron titanium oxide minerals, such as ilmenite. In the present invention, it is preferred to use titanium oxide minerals having no or only a low iron content, preferably not more than 10 wt.-% based on the total pigment weight, even more preferably not more than 8 wt.-% and most preferably not more than 5 wt.-% of iron oxide.

[0089] If a synthetic or natural mica pigment (C) containing a titanium oxide mineral is used, then based on the total weight of the synthetic or natural mica pigment (C), the weight of the mica content is preferably in the range of 55 wt.% to 90 wt.%, more preferably in the range of 60 wt.-% to 85 wt.-% and most preferably in the range of 65 wt.-% to 80 wt.-%, while the amount of titanium dioxide is preferably in the range of 10 wt.-% to 45 wt.-%, more preferably 15 wt.-% to 40 wt.-% and most preferably 20 wt.-% to 35 wt.-%.

[0090] The term "synthetic or natural mica pigment (C)" encompasses such coated and / or surface-treated pigments, and the total weight of such coated and / or surface-treated mica pigments should be understood as the weight of the "synthetic or natural mica pigment (C)". Thus, the weight includes the coating material.

[0091] The weight ratio of the flaky mica pigment (C) to the sum of the film-forming polymer (A1) and the crosslinking agent (A2), i.e., (C) / [(A1)+(A2)], is preferably in the range of 0.005 to 0.35, more preferably in the range of 0.010 to 0.30, even more preferably in the range of 0.015 to 0.25, and most preferably in the range of 0.020 to 0.20.

[0092] Such mica pigments (C) as used in the manufacture of the paint compositions of the present invention preferably have a volume-based D90 value of less than 55 μm, more preferably less than 45 μm; a volume-based D50 value of less than 35 μm, more preferably less than 30 μm or even less than 20 μm; and a volume-based D10 value of less than 20 μm, more preferably less than 15 μm; and preferably a flake thickness of 50 nm to about 400 nm, as determined by electron microscopy as described in the experimental section of this specification. In any case, D90 > D50 > D10. Particularly preferred D90 values are < 35 μm and > 20 μm, D50 values are < 20 μm and > 15 μm and D10 values are < 15 μm and > 3 μm; or D90 values are < 25 μm and > 15 μm, D50 values are < 15 μm and > 10 μm and D10 values are < 10 μm and > 3 μm.

[0093] Commercially available flaky LiDAR reflective mica pigments (C) are, for example, from Merck KGaA (Darmstadt, Germany) under the trade names and SW Silver GreyFine Satin and SW Silver Grey are available; or from SUN Chemical (DIC) under the trade names Mearlin CFS Bright Silver 1303Z and Mearlin CFS Fine Pearl 1303V are available.

[0094] Based on the total weight of the paint composition according to the present invention, the mica pigment (C) is preferably present in the range of 0.1 wt.-% to 6.0 wt.-%, more preferably in the range of 0.2 wt.-% to 5.0 wt.-%, even more preferably in the range of 0.3 wt.-% to 4.0 wt.-%, and most preferably in the range of 0.4 wt.-% to 3.0 wt.-%, such as 0.5 wt.-% to 2.5 wt.-%.

[0095] Component (D)

[0096] The coating composition of the present invention comprises water and / or one or more organic solvents as component (D), and component (D) is present in the coating composition in an amount that is the difference between the total weight of the composition and the weight of its solid content.

[0097] When the coating composition of the present invention mainly comprises water as the volatile component, it is named an aqueous or water-based composition. In this case, it is preferably a coating composition containing a smaller proportion of organic solvents.

[0098] All conventional organic solvents known to those skilled in the art can be used as the organic solvents for preparing the coating composition of the present invention. The term "organic solvent" is known to those skilled in the art, especially from Council Directive 1999 / 13 / EC of 11 March 1999. Preferably, one or more organic solvents are selected from the group consisting of: monohydric or polyhydric alcohols, such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, ethylene glycol, ethyl ethylene glycol, propyl ethylene glycol, butyl ethylene glycol, butyl diethylene glycol, 1,2-propanediol and / or 1,3-propanediol; ethers, such as diethylene glycol dimethyl ether; aliphatic hydrocarbons, aromatic hydrocarbons, such as toluene and / or xylene; ketones, such as acetone, N-methylpyrrolidone, N-ethylpyrrolidone, methyl isobutyl ketone, isophorone, cyclohexanone, methyl ethyl ketone; esters, such as methoxypropyl acetate, ethyl acetate and / or butyl acetate; amides, such as dimethylformamide, and mixtures thereof.

[0099] Optional additional component (E) of the coating composition

[0100] The coating composition of the present invention may optionally comprise one or more components (E), which are different from each of components (A1), (A2), (B), (C) and (D).

[0101] Depending on the desired application, the coating composition of the present invention may contain one or more commonly used additives (E). For example, the coating composition may comprise at least one additive selected from the group consisting of: reactive diluents (such as polypropylene glycol), light stabilizers, antioxidants, degassing agents, emulsifiers, lubricity-promoting additives, polymerization inhibitors, plasticizers, initiators for free radical polymerization, adhesion promoters, flow control agents, film-forming aids, sag control agents (SCA), flame retardants, corrosion inhibitors, desiccants, biocides, and / or matting agents. They can be used in known and customary proportions. Preferably, their content is from 0.01 wt.-% to 25 wt.-%, more preferably from 0.05 wt.-% to 20 wt.-%, particularly preferably from 0.1% to 15% by weight, most preferably from 0.1% to 10% by weight, especially from 0.1% to 7% by weight and most preferably from 0.1% to 5% by weight, based on the total weight of the coating composition according to the present invention.

[0102] Among these additives, the coating composition according to the present invention may optionally contain at least one thickener or rheology modifier. Examples of such thickeners are inorganic thickeners, such as metal silicates like phyllosilicates, and organic thickeners, such as poly(meth)acrylic acid thickeners and / or (meth)acrylic acid / (meth)acrylate copolymer thickeners, polyurethane thickeners, and polymeric waxes. The metal silicates are preferably selected from the group of montmorillonites. Montmorillonites are particularly preferably selected from the group of montmorillonite and hectorite. In particular, montmorillonite and hectorite are selected from the group consisting of aluminum-magnesium silicates and sodium-magnesium and sodium-magnesium fluoride-lithium layered silicates. These inorganic layered silicates are sold, for example, under the trade name The thickeners based on poly(meth)acrylic acid and (meth)acrylic acid / (meth)acrylate copolymer thickeners are optionally crosslinked and / or neutralized with a suitable base. Examples of such thickeners are "alkali-swellable emulsions" (ASE) and their hydrophobically modified variants, i.e., "hydrophobically modified alkali-swellable emulsions" (HASE). Preferably, these thickeners are anionic. Corresponding products such as are commercially available. The polyurethane-based thickeners (e.g., polyurethane associative thickeners) are optionally crosslinked and / or neutralized with a suitable base. Corresponding products such as are commercially available. Examples of suitable polymeric waxes are optionally modified polymeric waxes based on ethylene-vinyl acetate copolymers. Corresponding products are commercially available, for example, under the name

[0103] ​If at least one thickener is present in the coating composition according to the invention, it is preferably present in an amount of at most 10% by weight, more preferably at most 8% by weight, most preferably at most 4% by weight, in particular at most 2% by weight and most preferably not more than 1% by weight, in each case based on the total weight of the coating composition. The minimum amount of thickener is preferably 0.1% by weight in each case based on the total weight of the coating composition.

[0104] The further optional component (E) can also be a pigment different from the metallic effect pigment (B) and the mica pigment (C). Such pigments are used especially for coloring purposes, preferably only for coloring purposes.

[0105] If additional pigments (E) are included, they should preferably be LiDAR - reflective or LiDAR - transparent and in particular not LiDAR - absorptive.

[0106] If additional LiDAR - absorptive pigments (E), such as carbon black, are used in the paint according to the invention, they should preferably be included only in coloring amounts. As used herein, the term "coloring amount" means an amount preferably in the range from 0.005 wt.-% to 0.5 wt.-%, more preferably in the range from 0.01 wt.-% to 0.3 wt.-% and most preferably in the range from 0.015 wt.-% to 0.15 wt.-%, such as from 0.020 wt.-% to 0.10 wt.-%, based on the total weight of the paint composition according to the invention. However, the use of LiDAR - absorptive pigments is not preferred in the present invention because their use typically results in a reduction of the LiDAR reflectance ratio within the desired range of incident angles.

[0107] The additional LiDAR - reflective or LiDAR - transparent pigments (E) can be included in higher amounts preferably in the range from 0.01 wt.-% to 4.0 wt.-%, more preferably from 0.020 wt.-% to 2.5 wt.-%, even more preferably in the range from 0.025 wt.-% to 1.5 wt.-%, such as from 0.030 wt.-% to 1 wt.-%, based on the total weight of the paint composition according to the invention.

[0108] As used herein, a pigment (E) is considered a LiDAR - reflective pigment if, as detailed in the experimental section, by using an externally coated Metopac TM T12G test panel, measured on the black side of the panel, the pigment (E) shows at least 15% LiDAR reflectance; and if, as detailed in the experimental section, by using an externally coated Metopac TMThe T12G test panel, measured on the white side of the panel, shows at least 50% LiDAR reflectivity for the pigment (E). The measurement of the colored pigment (E) is carried out only at an angle of 0°.

[0109] Suitable LiDAR transparent pigments (E) are, for example, perylene-based pigments such as those available under the trade name BlackL0086 (formerly known as Black L0086), Black K0087 (formerly known as Black K0087) and Black EH8082, while suitable LiDAR reflective pigments (E) can be of the mixed metal oxide type and are available, for example, under the trade name Black L0095.

[0110] Typically, almost all organic colored pigments are LiDAR transparent and show similar behavior at 1550 nm. At 905 nm, some differences can be observed, for example, compared to Pigment Yellow 139 from Sun Chemical Corporation (DIC) Yellow L2145H, Pigment Blue 60 such as from Sun Chemical Corporation (DIC) Blue L 6480 performs poorly.

[0111] The preparation of the coating composition can be carried out using conventional and known preparation and mixing methods and mixing units, or using conventional dissolvers and / or stirrers.

[0112] Coating layer

[0113] A further subject of the present invention is a coating layer obtainable from the paint composition of the present invention, in particular by applying the coating composition of the present invention to a substrate, preferably according to the method of the present invention disclosed below.

[0114] All the preferred embodiments described above for the coating composition of the present invention and its preferred embodiments are also preferred embodiments of the coating layer of the present invention (i.e., the paint layer of the present invention).

[0115] Preferably, the paint layer of the present invention is at least partially present on the surface of the substrate, which is preferably coated with a light gray or white primer layer.

[0116] The coating of the present invention is capable of reflecting near-infrared (NIR) light having a wavelength of 700 to 1560 nm.

[0117] The method of the present invention for forming a coating layer and / or a multi-layer coating

[0118] A further subject of the present invention is a method for at least partially forming a coating layer on at least one surface of a substrate, wherein the method comprises at least step (a), namely

[0119] (a) At least partially applying the paint composition of the present invention to at least one surface of an optionally pre-coated substrate to form a paint layer on the surface of the substrate.

[0120] A further subject of the present invention is a method for at least partially forming a cured paint layer on at least one surface of a substrate, wherein the method comprises at least step (a) as defined above and at least step (b), namely

[0121] (b) Curing the paint layer obtained after carrying out step (a) to form a cured coating on the surface of the substrate.

[0122] If the substrate is pre-coated with a primer coating composition to form a primer coating, the primer coating is preferably light-colored, such as light gray or white. Preferably, the primer coating composition and thus the primer coating or primer coating layer contain titanium dioxide as the main pigment. The term "main" pigment means that the content of other pigments in the primer coating composition is not as high as that of the main pigment.

[0123] When the coating composition of the present invention is a - preferably aqueous - paint coating composition, step (a) or steps (a) and (b) are preferably carried out on at least one surface of the pre-coated substrate. If the substrate is a metal substrate, the metal substrate preferably has a primer and / or an electrodeposition coating as a pre-coating layer and / or a conversion coating as a pretreatment.

[0124] Irrespective of the substrate used, after carrying out step (a) or steps (a) and (b), preferably in step (c) a varnish composition is applied to the paint coating to form a varnish layer. The varnish can be cured separately or simultaneously with the paint layer, or simultaneously with the primer layer and the paint layer.

[0125] The inventors of the present invention have found that, with regard to LiDAR reflectivity, it is particularly preferred to use a varnish composition that produces a matte varnish layer. Such a varnish composition for forming a matte varnish layer contains one or more matting agents. The matting agent can be any known matting agent in the field of coatings, preferably selected from the group consisting of: synthetic silica gels, including precipitated silica gels and agglomerated-precipitated silica gels; natural silica gels, such as diatomaceous earth; silica gels treated with wax or polymers; waxes; talc; and micronized polymers, such as micronized urea-formaldehyde resins. More preferably, the matting agent is selected from the group consisting of: synthetic silica gels (including precipitated silica gels and agglomerated-precipitated silica gels) and silica gels treated with wax or polymers. Most preferably, the matting agent is selected from the group consisting of: silica treated with polymers, such as ACEMATT 3300 (Evonik), silica gels, such as SYLOID C 2006 (Grace) and / or precipitated silica post-treated with wax, such as ACEMATT OK 412 (Evonik). Based on the total weight of the varnish composition, the amount of the matting agent in such a varnish composition is preferably in the range of 0.1 wt.-% to 25 wt.-%, more preferably in the range of 0.5 wt.-% to 20 wt.-% and most preferably in the range of 1.0 wt.-% to 10 wt.-%, such as 2.0 wt.-% to 8 wt.-%.

[0126] Particularly preferred is a method for forming a multi-layer coating, which method comprises the following steps:

[0127] (a) applying at least partially the paint composition of the present invention to at least one surface of a substrate, which substrate is preferably coated with a filler coating layer that is preferably white or grey, more preferably white, to form a paint layer on the surface of the substrate; and

[0128] (b) applying a glossy or matte varnish composition, preferably a matte varnish composition, to the paint layer to obtain a varnish layer; and

[0129] (c) curing the paint layer before applying the varnish or curing the paint layer and the varnish layer simultaneously,

[0130] wherein at least one of a filler coating layer or a varnish layer is present.

[0131] Even more preferred is a method for forming a multi-layer coating, which method comprises the following steps:

[0132] (a) applying at least partially the paint composition of the present invention to at least one surface of a substrate, which substrate is coated with a filler coating layer that is preferably white or grey, more preferably white, to form a paint layer on the surface of the substrate; and

[0133] (b) Applying a glossy or matte, preferably matte, varnish composition onto the paint layer to obtain a varnish layer; and

[0134] (c) Curing the paint layer before applying the varnish or curing the paint layer and the varnish layer simultaneously.

[0135] Most preferably, a method for forming a multi-layer coating, which comprises the following steps:

[0136] (a) Applying at least partially the paint composition of the present invention onto at least one surface of a substrate coated with a white filler coating layer to form a paint layer on the surface of the substrate; and

[0137] (b) Applying a matte varnish composition onto the paint layer to obtain a varnish layer; and

[0138] (c) Curing the paint layer before applying the varnish or curing the paint layer and the varnish layer simultaneously.

[0139] The paint composition of the present invention, as well as the primer composition and / or the varnish composition, can be applied onto an object by many techniques well-known in the art, including spraying, drop coating, dip coating, roll coating, curtain coating, and other techniques. Preferably, the coating composition of the present invention is applied by spraying, more preferably by air spraying or electrostatic spraying. It can be applied wet-on-wet, but it is not necessary.

[0140] All the preferred embodiments described above regarding the coating composition of the present invention, the coating of the present invention, and its preferred embodiments are also the preferred embodiments of the method of the present invention for forming a (cured) coating.

[0141] Substrate

[0142] Another subject of the present invention is at least partially coated substrate obtainable by the method of the present invention.

[0143] If a metal substrate is used to produce a coated substrate, such metal is preferably steel, galvanized steel, aluminum, or an alloy of these. The metal substrate is preferably pre-treated and / or pre-coated, most preferably with a primer and / (or) an electrodeposition coating as a pre-coating layer and / (or) a conversion coating as a pre-treatment of the metal surface.

[0144] In addition, the substrate used can be a glass or textile substrate, especially glass.

[0145] If the substrate is a plastic (polymer) substrate, it can also be a pre-coated substrate, which, for example, has a primer coating, but it is not necessary.

[0146] If a plastic (polymer) substrate is used, preferably a thermoplastic polymer is used as such a substrate. Suitable polymers are poly(meth)acrylates (including poly(methyl)methacrylate, poly(methyl)butyl acrylate), polyethylene terephthalate, polybutylene terephthalate, polyvinylidene fluoride, polyvinyl chloride, polyesters (including polycarbonates and polyvinyl acetate), polyamides, polyolefins (such as polyethylene, polypropylene, polystyrene and also polybutadiene), polyacrylonitrile, polyacetals, acrylonitrile - ethylene - propylene - diene - styrene copolymer (A - EPDM), ASA (acrylonitrile - styrene - acrylate copolymer) and ABS (acrylonitrile - butadiene - styrene copolymer), polyetherimide, phenolic resin, urea resin, melamine resin, alkyd resin, epoxy resin, polyurethane (including TPU), polyether ketone, polyphenylene sulfide, polyethers, polyvinyl alcohol, and mixtures thereof. Polycarbonates and poly(meth)acrylates are particularly preferred. The substrate can also be a composite substrate, such as for example a fiber - reinforced substrate containing glass fibers, carbon fibers or polymer fibers such as polyamide fibers. The substrate can also consist of multiple polymer layers.

[0147] These coated substrates can be used for producing, for example, automotive bodies and parts thereof.

[0148] All preferred embodiments described above regarding the coating composition of the present invention, the coating layer of the present invention, and the method of the present invention for forming a coated film and a coating and their preferred embodiments are also preferred embodiments of the substrate of the present invention.

[0149] A method of at least partially forming a coating layer on at least one surface of a substrate - as defined above:

[0150] (a) At least partially applying the color paint composition of the present invention to at least one surface of an optionally pre - coated substrate to form a color paint layer on the surface of the substrate; and

[0151] (b) Curing the color paint layer obtained after performing step (a) to form a cured coating on the surface of the substrate,

[0152] Also suitable as a method for improving the LiDAR reflectivity and / or LiDAR detectability of an object, where the substrate is the object or becomes part of the object, which will be improved in terms of LiDAR reflectivity and / or LiDAR detectability.

[0153] Further preferred features and embodiments of the method for improving the LiDAR reflectivity and / or LiDAR detectability of an object are the same as those of the method for at least partially forming a coating layer on at least one surface of a substrate. This applies in particular with respect to the substrate, the filler coating composition or the primer coating composition and the varnish composition used in said method; and also with respect to the pretreatment and precoating of the substrate used in this method. Of course, any preferred features or embodiments of the paint composition of the present invention can be used in the method for improving the LiDAR reflectivity and / or LiDAR detectability. The application parameters and techniques are the same as those described for the method for at least partially forming a coating layer on at least one surface of a substrate.

[0154] Furthermore, a method for forming a multi-layer coating comprising the steps of:

[0155] (a) at least partially applying the paint composition of the present invention to at least one surface of a substrate, which substrate is preferably coated with a preferably white or grey, more preferably white filler coating layer, to form a paint layer on the surface of said substrate; and

[0156] (b) preferably applying a glossy or matte varnish composition, preferably a matte varnish composition, to the paint layer to obtain a varnish layer; and

[0157] (c) curing the paint layer before applying the varnish or curing the paint layer and the varnish layer simultaneously,

[0158] wherein there is at least one of a filler coating layer or a varnish layer,

[0159] is also suitable as a method for improving the LiDAR reflectivity and / or LiDAR detectability of an object, wherein the substrate is the object or becomes part of the object, which will be improved in terms of LiDAR reflectivity and / or LiDAR detectability.

[0160] Further preferred features and embodiments of the method for improving the LiDAR reflectivity and / or LiDAR detectability of an object are the same as those of the method for at least partially forming a multi-layer coating on at least one surface of a substrate. This applies in particular with respect to the substrate, the filler coating composition or the primer coating composition and the varnish composition used in said method; and also with respect to the pretreatment and precoating of the substrate used in this method. Of course, any preferred features or embodiments of the paint composition of the present invention can be used in the method for improving the LiDAR reflectivity and / or LiDAR detectability. The application parameters and techniques are the same as those described for the method for at least partially forming a multi-layer coating on at least one surface of a substrate.

[0161] Use

[0162] Another subject of the present invention is the use of the coating of the present invention and / or the at least partially coated substrate of the present invention and / or the object produced from said substrate in LiDAR visibility applications, in particular for autonomous driving systems such as autonomous vehicles and vehicles with ADAS. Of course, the coating material can also be applied to non-autonomous vehicles and their parts to make such vehicles and their parts LiDAR-reflective to be detected by other vehicles such as autonomous vehicles.

[0163] All the preferred embodiments described above with respect to the coating composition of the present invention, the coating film of the present invention, the coating of the present invention, and the method of the present invention for forming the coating film and the coating and the at least partially coated substrate of the present invention and their preferred embodiments are also preferred embodiments of the use of the present invention.

[0164] The use of the present invention benefits from better infrared light and LiDAR visibility, especially for autonomous driving systems such as autonomous vehicles and vehicles with ADAS.

[0165] Examples

[0166] Methods

[0167] Determination of solid content

[0168] The non-volatile fraction (solid content) is determined in accordance with DIN EN ISO 3251 (date: June 2008). This involves weighing 1 g of the sample into an aluminum dish that has been pre-dried, drying it in an oven at 125 °C for 60 minutes, cooling it in a desiccator, and then reweighing it. The residue corresponds to the non-volatile part relative to the total amount of the sample used. Optionally, the volume of the non-volatile part can be determined according to DIN 53219 (date: August 2009) if necessary.

[0169] Volume-based D10, D50, and D90 values

[0170] The above parameters are determined by dynamic light scattering using the above Malvern Zetasizer (from Malvern, S90 unit, nano series model ZEN 1690 mfg 5 / 2017). For the measurement, the pigment dispersion is diluted with an appropriate solvent (deionized water for aqueous dispersions and organic solvents for solvent-based dispersions) to a photon count rate of no more than about 300 to 500 counts when the unit is placed on an attenuator set to 7. The operating temperature is maintained at 25 °C ± 1 °C and the sample size is about 10 to 15 mL (square glass cuvette).

[0171] The procedure is as follows:

[0172] Typically, if 0.07 g of a paste containing 20 wt.-% pigment is first diluted to 15.0 g of deionized water and then 5 drops of this solution are further diluted to 15.0 g of deionized water, the photon counting rate is within the above range. If the pigment paste contains more or less than 20 wt.-% pigment, the initial amount of 0.07 g should be decreased or increased accordingly.

[0173] Using such twice-diluted paste, the volume-based D10, D50, and D90 values are determined.

[0174] Determination of the flake thickness of pigments

[0175] The flake thickness can be determined as follows: First, the flake pigment is dispersed in a suitable solvent and incorporated into a paint composition. Then, the paint composition containing the flake pigment is sprayed onto a substrate and cured. The film thus obtained is peeled off from the sample edge and small pieces of the film are cut using a diamond knife by a microtome, and the flakes are transferred onto a TEM grid. The flakes are examined on a STEM or TEM to determine the thickness of the corresponding flake pigment.

[0176] Determination of the LiDAR reflectivity of mica pigment (C) and additional pigment (E)

[0177] To determine the LiDAR reflectivity of the pigment, a coating is prepared and applied as follows:

[0178] Use a Metopac TM T12G test panel as the substrate (which is also widely used in ASTM D6441). The luminance value L of the black part of the panel is 3.60 at a 15° angle in the Lab system, while the luminance value L of the white part of the panel is 94.08 at a 15° angle in the Lab system.

[0179] Disperse an effect pigment such as mica pigment (C) or other flake pigments such as glass flakes (E) in a standard coating composition as described in Table A, and then apply the dispersion in multiple tones onto the Metopac TM T12G test panel to obtain a dry layer thickness of 17.5 ± 2.5 μm at a pigment-to-binder ratio of 0.2. The LiDAR reflectance is measured based on the incident angle on both the white and black parts of the substrate.

[0180] Another pigment (E), especially a colored pigment (E), is dispersed and applied in the same manner as the effect pigment, however, a dry layer thickness of 20 μm is obtained at a pigment-to-binder ratio of 0.3. The LiDAR reflectance of the colored pigment (E) is measured only at an incident angle of 0° (perpendicular) on both the white and black parts of the substrate.

[0181] As used throughout the present invention and in accordance with EN ISO 4618:2006 (German version), the term "binder" means the solid content (i.e., non-volatile content) without pigments and fillers. In this context, layered silicates and silica are considered fillers, although they may have additional properties such as thickening properties.

[0182] Subsequently, and prior to measurement, a varnish layer containing a UV stabilizer (formed from a polyol and an isocyanate hardener (ProGloss)) with a dry film thickness of approximately 50 μm is applied and cured.

[0183] The angular-dependent LiDAR reflectivity of the samples is measured using a Velodyne VLP-16 LiDAR sensor fired at 905 nm. The sensor is mounted at a distance of approximately 1 m from the sample and is moved along a circular path around the center of the sample such that the angle of incidence of the LiDAR radiation on the sheet varies from 0° to 60° in 5° steps.

[0184] The LiDAR reflectivities of the different micas (C) and additional pigments (E) determined as above are shown in Table B.

[0185] Preparation of the Coated Substrate

[0186] Test panels were prepared as follows. Cold-rolled steel panels pretreated by conversion coating and pre-coated with a cathodic electrodeposition coating composition (zinc phosphate-coated CRS panels, electroplated as specified in Table 1) were spray-coated with a white or gray primer by ESTA. The primer layer thus obtained was cured at 160 °C for 20 minutes. The primer layer thus obtained had a dry layer thickness of approximately 25 μm.

[0187] On the primer layer thus obtained, color paint compositions C and E1 to E13 (constituted as described in Tables 2 and 3; the characteristics of the mica pigments (C) and additional pigments (E) are shown in Table B, and the characteristics of the aluminum effect pigments (B) are shown in Table C) were applied by spraying. After flash-off at 80 °C for 10 min, the color paint layer thus obtained had a dry layer thickness of approximately 12 μm.

[0188] On the color paint layer thus obtained, a varnish composition (constituted as described in Table 4) was applied by spraying ESTA. The varnish layer thus obtained was cured at 140 °C for 17 minutes. The varnish layer thus obtained had a dry layer thickness of approximately 40 μm.

[0189]

[0190]

[0191] ​

[0192]

[0193]

[0194]

[0195]

[0196] Result

[0197] Table 5 shows the LiDAR reflectance of different inventive paint compositions E1 to E6 compared to the comparative paint composition C without LiDAR - reflective mica pigment (C) (these compositions are those as described in Table 2).

[0198] Compared to comparative example C, all inventive examples E1 to E6 show a significant improvement in the LiDAR reflectance of the multilayer coating at higher and relevant angles of incidence from 25° to 45°, especially at 25° and 40°.

[0199] Comparison of E1 with E3 shows that synthetic mica and natural mica have almost the same behavior in the range of angles of incidence from 30° to 45°.

[0200] Comparison of E1 with E4 and especially E3 with E5 shows that the reduction of the amount of phthalocyanine colorant from 0.021 wt.-% to 0.011 wt.-% also results in a further overall improvement in LiDAR reflectance.

[0201] Comparison of E4 (1.5 wt.-% synthetic mica 1) and E6 (1.5 wt.-% synthetic mica 1 and 0.506 wt.-% glass flakes) shows that, especially in the upper range of the angle of incidence, the use of glass flakes instead of synthetic mica 1 results in a smaller improvement in LiDAR reflectance.

[0202] Comparison of E1 with E2 shows that the presence of iron oxide in addition to a large amount of titanium oxide in the coating of synthetic mica results in a decrease in LiDAR reflectance, while there is still an improvement for 25° and 40° angles.

[0203] Table 5 - Paint Compositions from Table 2 on a Gray Primer

[0204]

[0205] Table 6a clearly shows that using a LiDAR-transparent perylene colorant (PB32; 0.037 wt.-%) with a coloring amount in Example E8 instead of a LiDAR-absorbing carbon black (PB7; 0.030 wt.-%) with a coloring amount in Example E7 results in a strong improvement in LiDAR reflectivity. Therefore, it is preferred to avoid using carbon black or other significantly LiDAR-absorbing pigments.

[0206] Examples E7, E9, and E10 containing carbon black mainly differ in the amount of mica pigment (C). In all three examples, 0.5 wt.-% of natural mica 2 is used. However, in Example E9, an additional 0.5 wt.-% of natural mica 3 is used, and in Example E10, an additional 1.0 wt.-% of natural mica 3 is used. Using more mica pigment (C) in Examples E9 and E10 results in an increase in reflectivity.

[0207] Table 6a - Paint compositions from Table 3 on a gray primer

[0208]

[0209] Table 6b shows a comparison of three different multi-layer coatings E11, E12, and E13 each on white and gray primers, which are constituted as shown in Table 1. It was found that even better reflectivity exists in the range of incident angles from 25° to 45° when using a white primer instead of a gray primer. In addition, it was observed that increasing the amount of natural mica 3 from 1.5 wt.-% (E12) to 2.0 wt.-% (E13) results in a further improvement in LiDAR reflectivity.

[0210] Table 6b - Paint compositions from Table 3 on a gray or white primer

[0211] In Table 7, two multi-layers both containing the same gray primer layer and the same paint layer of the present invention are compared, which only differ in using a glossy varnish (E14) and a matte varnish (E15) respectively, and these varnishes are constituted as shown in Table 4.

[0212] Table 7 - Matte varnish vs. glossy varnish

[0213]

Claims

1. A color paint composition, the color paint composition comprising: (A) at least one film-forming polymer (A1), and in the case where (A1) is externally crosslinkable, at least one crosslinking agent (A2); (B) at least two types of metallic effect pigments (B); and (C) at least one type of LiDAR reflective mica pigment (C), (D) water and / or one or more organic solvents as component (D).

2. The color paint composition according to claim 1, wherein The film-forming polymer (A1) is selected from the group of polymers consisting of: polyurethanes, polyureas, polyesters, polyamides, poly(meth)acrylates and / or copolymers of the structural units of said polymers; and if (A1) is externally crosslinkable, then (A2) is selected from the group of crosslinking agents consisting of: aminoplast resins, blocked polyisocyanates and free polyisocyanates.

3. The color paint composition according to claim 1 or 2, wherein At least one of these metallic effect pigments (B) is selected from corn flake aluminum pigments; and it is characterized in that at least one of these metallic effect pigments (B) is selected from silver dollar aluminum pigments.

4. The color paint composition according to any one of the preceding claims, wherein These metallic effect pigments have a volume-based D90 value of less than 60 μm; a volume-based D50 value of less than 40 μm; and a volume-based D10 value of less than 25 μm; and / or a flake thickness in the range from 150 nm to 1000 nm.

5. The color paint composition according to any one of the preceding claims, wherein The difference between the particle size distribution spans of the metallic effect pigment (B) having the largest particle size distribution span and the metallic effect pigment (B) having the smallest particle size distribution span is in the range from 0.2 to 1.0, and the particle size distribution span of each metallic effect pigment (B) is according to the formula [(D90 - D10) / (D50)] from the volume-based D90, D50 and D10 values.

6. The color paint composition according to any one of the preceding claims, wherein The total amount of the metallic effect pigment (B) in the color paint composition ranges from 0.2 wt.-% to 8.0 wt.-% based on the total weight of the color paint composition.

7. The color paint composition according to any one of the preceding claims, wherein The at least one type of LiDAR reflective mica pigment (C) is selected from natural or synthetic mica which is uncoated or coated with one or more oxides.

8. The color paint composition according to any one of the preceding claims, wherein The main component in component (D) is water.

9. The color paint composition according to any one of the preceding claims, wherein The color paint composition further comprises one or more types of pigments (E), which are different from pigments (B) and (C), and the pigments (E) are selected from the group of colored LiDAR reflective pigments or colored LiDAR transparent pigments.

10. The color paint composition according to any one of the preceding claims, wherein The solids content based on the total weight of the color paint composition is in the range from 10 wt.-% to 35 wt.-%.

11. A method for at least partially forming a coating layer on at least one surface of a substrate, wherein the method at least includes step (a), that is (a) applying at least partially the color paint composition as defined in any one of the preceding claims to at least one surface of an optionally pre-coated substrate to form a coating film on this surface of the substrate.

12. The method for forming a coating layer according to claim 11, the method comprising the following steps: (a) At least partially applying the color paint composition as defined in any one of the preceding claims to at least one surface of an optionally pre-coated substrate to form a coating film on the substrate, the coating film being a color paint layer and the pre-coated substrate being a substrate coated with a filler layer; and (b) Optionally applying a varnish composition to the color paint layer to obtain a varnish layer; and (c) Curing the color paint layer before applying the optional varnish composition or curing the color paint layer and the varnish layer simultaneously, wherein at least one of the filler layer or the varnish layer is present.

13. A method for improving the LiDAR reflectivity and / or LiDAR detectability of an object, the method comprising the steps according to any one or more of claims 11 or 12, wherein, The substrate is the object or forms part of the object, which will be improved in terms of LiDAR reflectivity and / or LiDAR detectability.

14. A coating layer obtainable from a coating composition according to any one of claims 1 to 10 or obtained by a method according to any one of claims 11 to 13.

15. At least partially coated substrate obtainable by a method according to any one of claims 11 to 13.

16. Use of the at least partially coated substrate according to claim 15 in LiDAR visibility applications related to vehicles and their parts.

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