Coating composition for forming coating film that is easily detectable by lidar sensor and coating film

Abstract

To provide a coating composition for forming a coating film and coating film that can improve the detection accuracy of location information in tunnels for LiDAR sensors by forming a coating film with diffuse reflectance properties as a coating film used to protect the surface of tunnel structures for autonomous vehicles equipped with LiDAR sensors that travel through tunnels.SOLUTION: A coating for forming a coating film of the invention that is easily detectable by a LiDAR sensor formed on the inner wall of a tunnel is composed of: a primer coating for forming a coating film that contains near-infrared reflective pigments in a resin component serving as a binding agent; and a top coating for forming a coating film that contains light-diffusing fine particles formed from polymerizable monomers in a silicone resin serving as a binding agent.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a coating composition for forming a coating film, and a coating film that can improve the detection accuracy of position information inside a tunnel for a LiDAR (Light Detection And Ranging) sensor by forming a coating film having diffuse reflectivity as a coating film used for protecting the surface of a tunnel structure for an autonomous vehicle equipped with a LiDAR sensor that travels inside the tunnel. [Background technology]

[0002] Methods for estimating the vehicle's own position for autonomous vehicles include detecting magnetic markers embedded in the road surface using sensors installed on the vehicle, estimating the position using a global navigation satellite system (GNSS), and referencing the position using a three-dimensional point cloud map and LiDAR. However, there are issues in that GNSS cannot be received in tunnel sections, and because the shape of the tunnel is monotonous, the longer the distance, the greater the position error in the three-dimensional point cloud map becomes. In addition, in order for autonomous vehicles to detect other vehicles, pedestrians, obstacles, etc. on the road and decelerate, it is necessary to be able to detect them over a wider distance, quickly, and with high accuracy.

[0003] LiDAR sensors are a technology that emits laser light and measures the distance to an object and the shape of the object based on the information of the reflected light. They can detect people and obstacles with higher accuracy than radars that use millimeter waves with frequencies of 30 to 300 GHz, and are therefore widely used in systems that support autonomous driving. LiDAR sensors often use near-infrared light with wavelengths of 905 to 1550 nm, and in order to be easily detected by LiDAR sensors, optical properties that make it difficult to absorb light in this wavelength range and reflect it more efficiently are required. For this reason, there is a demand for the development of paints or coatings that are optimal for LiDAR sensors.

[0004] For example, Patent Document 1 (JP 2021-075454 A) discloses an invention relating to black titanium dioxide LiDAR reflective particles and a vehicle having the same that can improve the obstacle detection sensitivity of self-driving vehicles that use LiDAR sensors. The invention disclosed in this Patent Document 1 describes black titanium dioxide that contains a crystalline titanium dioxide core and an amorphous titanium dioxide shell that encapsulates the crystalline titanium dioxide core, and has a reflectance of 15% or less for electromagnetic radiation in the visible spectrum and a reflectance of 10% or more for near-infrared electromagnetic radiation and LiDAR electromagnetic radiation, as well as paints and coatings using the same (claims 1 and 16, examples 1 and 2, and Fig. 1B). It also discloses that a system for detecting and avoiding obstacles in an autonomous vehicle has been tested using a LiDAR system that uses pulsed laser electromagnetic radiation with a wavelength of 905 nanometers (paragraph 0002), and that the LiDAR-reflective black TiO2 particles can be detected by a LiDAR system that uses near-infrared electromagnetic radiation or LiDAR electromagnetic radiation of 905 nm or 1550 nm (paragraphs 0060 and 0061).

[0005] Furthermore, Patent Document 2 (Japanese Patent No. 7178059) discloses an invention of a coating composition for an object to be detected by a LiDAR sensor, which comprises a coating film-forming resin (A) and a colored pigment (B), wherein the colored pigment (B) comprises at least one of a white color pigment having a near-infrared reflectance of 60% or less and a chromatic color pigment having a near-infrared reflectance of 50% or more, an arbitrary amount of a black pigment having a near-infrared reflectance of 30% or more, and an organic pigment, a near-infrared reflective pigment (B1), wherein the content of the organic pigment is 3 mass% or more of the total amount of the near-infrared reflective pigment (B1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-075454 [Patent Document 2] Patent No. 7178059 Summary of the Invention [Problem to be solved by the invention]

[0007] According to the invention disclosed in Patent Document 1, it is possible to provide a paint that can improve the detection accuracy of vehicles (see claims 19 and 20) using a LiDAR sensor. Also, according to the invention disclosed in Patent Document 2, it is possible to form a paint composition and a coating film that can improve the detection accuracy of structures that may be obstacles during automatic driving of a car using a LiDAR sensor, such as various road structures such as vehicles, pavements, road markings, sidewalks, crosswalks, drainage facilities, at-grade intersection structures, and bridges.

[0008] On the other hand, in order to enable LiDAR sensors to detect the inner wall surface of a tunnel with high accuracy, it is necessary to increase the reflected light intensity at acute angles with a reflection angle of 90° or less with respect to the inner wall surface. However, Patent Document 1 does not suggest using this as paint for the inner walls of a tunnel, and Patent Document 2 also suggests using this as paint for the inner walls of a tunnel (see paragraph 0144), but does not disclose any specific conditions or characteristics for application to the inner walls of a tunnel.

[0009] The inventors have been studying the composition of the coating film formed on the inner wall surface of a tunnel that can be detected with high accuracy by a LiDAR sensor. The coating film on the inner wall surface of a tunnel to be compatible with such a LiDAR sensor corresponds to the "automatic operation support facility" in the "accessory of a road" listed in Article 2, Paragraph 2, Item 5 of the Road Law, so it is necessary to prevent the coating film part of the existing inner wall surface of the tunnel from attracting general drivers, and it is also required to have the same color and gloss as the coating film part of the existing inner wall surface of the tunnel. As a result, by forming a coating film with a multi-layer structure consisting of a specific undercoat coating film containing a near-infrared reflective material and not containing an organic pigment, and a topcoat coating film containing specific light-diffusing fine particles, it is possible to satisfy the regulations of the Road Law, while improving the diffuse reflection of near-infrared rays, and the reflection intensity of near-infrared rays can be increased even at a reflection angle of 45° or less, so that the inner wall surface of the tunnel can be detected with high accuracy by a LiDAR sensor, and the present invention has been completed.

[0010] In other words, the present invention aims to provide a coating composition for forming a coating film and a coating film that are easily detectable by a LiDAR sensor, thereby enabling an autonomous vehicle equipped with a LiDAR sensor traveling through the tunnel to detect the inner wall surface of a tunnel with high accuracy by forming a coating film with a specific multi-layer structure on the inner wall surface of a tunnel. [Means for solving the problem]

[0011] According to the present invention, there is provided a coating composition for forming a coating film formed on the inner wall surface of a tunnel, which is easily detectable by a LiDAR sensor, characterized in that it comprises a paint for forming an undercoat coating film in which a near-infrared reflective pigment is blended into a resin component serving as a binder, and a paint for forming a topcoat coating film in which light-diffusing microparticles formed from a polymerizable monomer are blended into a silicone resin serving as a binder.

[0012] In the coating composition for forming a coating film that is easily detectable by the LiDAR sensor of the present invention, the undercoat coating film forming paint contains a resin component as a binder and a near-infrared reflective pigment.

[0013] Resin components as binders of paints for forming undercoat coating films can be used as long as they have good dispersibility of near-infrared reflective pigments and good transmittance of near-infrared rays. Examples of resin components include acrylic resins, acrylic silicone resins, urethane resins, acrylic-modified urethane resins, urethane-modified acrylic resins, silicone resins, and modified silicone resins. These resin components as binders may be used alone or in combination of two or more. Among these resin components, acrylic silicone resins are preferred because they have excellent adhesion to silicone resins as binders of topcoat coating films. Examples of acrylic silicone resin raw materials that can be used include acrylic silicone emulsions such as Boncoat SA-6360 (trade name, manufactured by DIC Corporation) and LDM7523 (trade name, manufactured by Japan Coating Resins Corporation).

[0014] In addition, when the undercoat coating film forming paint is a water-based paint, the solvent can be water or a mixture of water and a water-soluble organic solvent. In this case, the organic solvent can be, for example, lower alcohols such as methanol, ethanol, and isopropanol. Furthermore, when the undercoat coating film is a solvent-based paint, for example, aromatic hydrocarbon solvents such as benzene, toluene, and xylene; aliphatic hydrocarbon solvents such as n-hexane, cyclohexane, octane, and isononane; alcohol solvents such as ethanol, isopropanol, and butanol; ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ester solvents such as ethyl acetate and butyl acetate; and ether solvents such as propylene glycol monomethyl ether and ethylene glycol monobutyl ether can be used.

[0015] In addition, the near-infrared reflective pigment contained in the paint for forming the undercoat coating film is preferably a combination of white and black pigments in order to be able to handle both new construction and existing renovations, since even if white is used as the coating film formed on the inner wall of a tunnel when it is newly constructed, it will turn gray due to changes over time such as dirt. Note that, although there are inorganic near-infrared reflective pigments and organic near-infrared reflective pigments, inorganic near-infrared reflective pigments are preferred because they have excellent reflectivity for light in the near-infrared region used in LiDAR.

[0016] Examples of inorganic white pigments include infrared shielding titanium oxide JR-1000 (trade name, manufactured by Teika Co., Ltd.), TIPAQUE CR-97, TIPAQUE CR-95 (all trade names, manufactured by Ishihara Sangyo Kaisha, Ltd.), and Typepure R-902 (trade name, manufactured by DuPont). Examples of inorganic black pigments include Typepace Black SG-101 (trade name, manufactured by Ishihara Sangyo Kaisha, Ltd., (Ca,Ti,Mn)O3), TM Black 3550 (trade name, Cu(Fe,Mn)O4, manufactured by Dainichi Seika Chemicals Co., Ltd.), IRR Black 6340 (trade name, (Fe,Cr)O x and those made of composite oxides such as those manufactured by Asahi Kasei Corporation. Since these inorganic white pigments and inorganic black pigments are both near-infrared reflective pigments, it is possible to provide substantially the same near-infrared reflectivity whether the color of the undercoat film is white or gray.

[0017] The content of the near-infrared reflective pigment in the paint for forming the undercoat coating film may be adjusted by increasing the content of the inorganic white pigment so that the color corresponds to the color of the tunnel inner wall at the time of new construction or repair, and adding the content of the inorganic black pigment so that the color of the tunnel inner wall at the time of repair is a predetermined brightness. The minimum content of the inorganic white pigment is preferably 20% by mass or more with respect to the total amount of the paint for forming the undercoat coating film from the viewpoint of improving the near-infrared reflectance of the undercoat coating film, and the upper limit is preferably 30% by mass or less from the viewpoint of improving adhesion with the topcoat coating film and maintaining workability when forming the undercoat coating film. Similarly, the minimum content of the inorganic black pigment varies depending on the brightness required at the time of new construction, but since a completely white color is not desired, it is preferably 1% by mass or more with respect to the total amount of the paint for forming the undercoat coating film, and the upper limit varies depending on the extent to which the paint is applied to the tunnel inner wall that has changed over time, but since it is considered that the entire tunnel wall will be repainted when it becomes too dirty, it is considered that a content of 10% by mass or less will be possible for repairing most of the tunnel inner walls. Therefore, it is considered that the preferred content of the inorganic white pigment as a near-infrared reflective pigment is 20 to 30 mass % relative to the total amount of the paint for forming the undercoat coating film, and the preferred content of the inorganic black pigment is 1 to 10 mass %.

[0018] In addition, additives such as pigments other than the near-infrared reflective pigment, ultraviolet absorbers, antioxidants, leveling agents, matting agents, mildew inhibitors, antistatic agents, rust inhibitors, dispersants, defoamers, thickeners, antifreeze agents, film-forming aids, etc. may be added to the paint for forming the undercoat film as necessary. In particular, Adekanol UH-420 and UH472 (both trade names, manufactured by Adeka Corporation) may be used as thickeners, and Texanol (2,2,4-trimethyl-1,3-pentanediol monoisobutyrate), butyl cellosolve, propylene glycol monomethyl ether acetate, etc. may be used as film-forming aids.

[0019] The undercoat paint having such a composition can be prepared by mixing the resin component as the binder, the near-infrared reflective pigment, the solvent, and additives added as necessary. In this case, from the viewpoint of uniformly dispersing the near-infrared reflective pigment in the undercoat paint, it is preferable to disperse the near-infrared reflective pigment using a dispersing machine such as a roll mill, a bead mill, a ball mill, or a dissolver.

[0020] The method of applying the paint for forming an undercoat coating film to the inner wall surface of a tunnel may be, for example, an air spray method, a roller coating method, etc. The thickness of the undercoat coating film formed after drying is generally about 20 to 50 μm. After applying the paint for forming an undercoat coating film to the inner wall surface of a tunnel, the undercoat coating film of the present invention can be formed by leaving it in the air for about half a day to a day for natural drying.

[0021] The coating composition for forming a coating film having easy detection by the LiDAR sensor of the present invention contains a paint for forming a topcoat coating film for forming a topcoat coating film for causing diffuse reflection (dispersed reflection) of near-infrared light reflected by the near-infrared reflective pigment in the undercoat coating film on the surface of the undercoat coating film formed on the inner wall surface of the tunnel so that the component reflected in the direction along the inner wall surface of the tunnel increases. As the paint for forming a topcoat coating film, a paint containing light-diffusing fine particles formed from a polymerizable monomer in a silicone resin as a binder is used.

[0022] Silicone resins include those generally referred to as organopolysiloxanes, silicone oligomers, etc., room temperature curing types, and those that react with curing agents or curing catalysts, and also include organopolysiloxanes mixed with alkoxysilanes as silane coupling agents, etc. These silicone resins, curing agents, and curing catalysts can be appropriately selected from commercially available products.

[0023] Furthermore, the light-diffusing fine particles formed from the polymerizable monomers blended in the paint for forming the topcoat coating film are obtained by synthesizing fine particles to be the nuclei (seeds) in advance, and forcibly supplying the monomers to the particles to polymerize them, and are already known in the art. As the light-diffusing fine particles formed from the polymerizable monomers, the Techpolymer (registered trademark) MBX series, which are cross-linked polymethylmethacrylate fine particles, the Techpolymer SBX series, which are cross-linked polystyrene fine particles, and the Techpolymer MSX (SMX) series, which are cross-linked polymethylmethacrylate-styrene copolymer fine particles (all of which are trade names, manufactured by Sekisui Chemical Co., Ltd.), can be used.

[0024] The lower limit of the preferred content ratio of the light diffusing microparticles formed from the polymerizable monomer blended in the paint for forming a topcoat coating film is not necessarily critical because it varies depending on the composition and components of the silicone resin used as the binder, but if it is too small, the near-infrared light diffuse reflection efficiency becomes too low and easy detection by a specified LiDAR sensor cannot be achieved, so it is preferable that the content is 1.0 mass% or more with respect to the total amount of binder constituting the topcoat coating film (including the binder using a hardener). Similarly, the upper limit is preferably 20.0 mass% or less from the viewpoint of workability when forming a topcoat coating film using the paint for forming a topcoat coating film.

[0025] By including light-diffusing particles formed from polymerizable monomers in the coating material for forming a coating film, the near-infrared light irradiated from the LiDAR sensor to the inner wall surface of the tunnel is diffusely reflected by the light-diffusing particles formed from the polymerizable monomers in the topcoat coating film, and the near-infrared light reflected by the inorganic near-infrared reflective pigment in the undercoat coating film is also diffusely reflected, so that the light is diffusely reflected over a wide angle range. Therefore, according to the coating film having a multi-layer structure formed using the coating composition for forming a coating film that is easily detectable by the LiDAR sensor of the present invention, the reflection intensity of the near-infrared light is strong even at an incident angle of 45° or less, so that the LiDAR sensor can detect the inner wall surface of the tunnel with high accuracy.

[0026] Other known light-diffusing microparticles include, for example, glittering pigments such as aluminum pigments or stainless steel pigments. However, since these are flake- or scale-like, they have good near-infrared reflectivity but poor diffuse reflection, and therefore are not suitable as diffuse near-infrared reflectors for the topcoat coating of the present invention.

[0027] Examples of methods for applying the coating material for forming a coating film include air spraying and roller coating. After applying the topcoat, the formed coating film can be dried to form a transparent glassy coating film. The formed coating film can be dried by leaving it in the air. The thickness of the formed topcoat film after drying is preferably about 3 to 20 μm.

[0028] According to the multi-layer coating film formed using the coating composition for forming a coating film having the ease of detection by the LiDAR sensor of the present invention obtained as described above, the near-infrared light emitted from the LiDAR of an autonomous vehicle in a tunnel is reflected by the inorganic near-infrared reflective pigment contained in the undercoat coating film formed on the inner wall surface of the tunnel, and this reflected light is diffused by the light-diffusing fine particles formed from the polymerizable monomer blended in the topcoat coating film, so that even with an incident angle of 45° or less, the amount of diffusely reflected light increases. As a result, the amount of diffusely reflected light returning to the autonomous vehicle side increases among the near-infrared light emitted from the LiDAR sensor installed in the autonomous vehicle traveling in the tunnel and irradiated to the inner wall surface of the tunnel, so that the detection accuracy of the position information in the tunnel detected by the LiDAR sensor is improved.

[0029] Moreover, since the topcoat coating film is made of an inorganic glassy film, the adhesion to the undercoat coating film is extremely good, especially when the resin component of the undercoat coating film is an acrylic silicone resin, and furthermore, exhaust gas and dirt are less likely to adhere to the inner wall of the tunnel, and the coating film also has protective properties and durability against neutralization, salt damage, frost damage, etc., and is non-flammable. Therefore, even if a coating film having a multi-layer structure formed using the coating composition for forming a coating film having easy detection by a LiDAR sensor of the present invention is applied to the surface protection of not only the inner wall of a tunnel, but also exposed concrete walls, enclosed space walls, various structures, various materials, etc., it is difficult for dirt to adhere due to exhaust gas and rainfall, and furthermore, it is a coating film having easy detection by a LiDAR sensor that is environmentally friendly because no harmful substances are generated when it is disposed of or incinerated.

[0030] In addition, by appropriately changing the content ratio of the inorganic near-infrared reflective pigments, namely, white pigments and black pigments, in the paint for forming the undercoat coating film, it is possible to prevent the coating film on the inner wall surface of an existing tunnel from attracting the attention of general drivers, thereby making it possible to provide a coating film forming paint composition and coating film that meets the regulations of the Road Act while being easily detectable by a LiDAR sensor that can detect the inner wall surface of a tunnel with high accuracy. Effect of the Invention

[0031] As described above, according to the present invention, it is possible to provide a coating composition for forming a coating film and a coating film that are easily detectable by a LiDAR sensor and can detect the inner wall surface of a tunnel with high accuracy using a LiDAR sensor. [Brief description of the drawings]

[0032] [Figure 1] Figures 1(a) to (c) are side views showing painted pieces positioned so that the angles of incidence are 90°, 45°, and 20°, respectively, and Figures 1(A) to (C) are plan views corresponding to Figures 1(a) to (c), respectively. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] The coating composition for forming a coating film and the coating film having the easy detection by the LiDAR sensor according to the present invention will be described in detail below using examples and various comparative examples. However, the examples shown below are examples for embodying the technical idea of ​​the present invention, and are not intended to limit the present invention to those shown in these examples. The present invention can be equally applied to other embodiments included in the scope of the claims.

[0034] [Creating the undercoat] The paint for forming the undercoat coating film common to the examples and comparative examples 1 to 3 was prepared as follows. First, 50 g of acrylic silicone emulsion Boncoat SA-6360 (trade name, manufactured by DIC Corporation), 2.0 g of Texanol (2,2,4-trimethyl-1,3-pentanediol monoisobutyrate) as a film-forming aid, 1.0 g of Adekanol UH-420 as a thickener, 18.0 g of ion-exchanged water, 25.0 g (corresponding to 25.0% by mass of the total amount of the paint for forming the undercoat coating film) of inorganic white pigment Typek PFR404 (trade name, manufactured by Ishihara Sangyo Kaisha, Ltd.) as a near-infrared reflective white pigment, and 4.0 g (corresponding to 4.0% by mass of the total amount of the paint for forming the undercoat coating film) of inorganic black pigment Typek Black SG-101 as a near-infrared reflective black pigment were placed in a 500 mL beaker and thoroughly stirred with a dissolver to prepare the paint for forming the undercoat coating film. This paint for forming a primer coating was sprayed onto one surface of a cold-rolled steel plate measuring 75 mm in length, 150 mm in width, and 4 mm in thickness using an air spray method so that the thickness after drying would be approximately 30 μm.The plate was then left to dry naturally in the atmosphere for half a day, creating samples with primer coatings for the four examples and comparative examples 1 to 3.

[0035] [Creating topcoat film] The topcoat coating paints of the Examples and Comparative Examples 1 to 3 were prepared as follows: 95.0 g of KR-500 (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.), a medium polymerization degree methyl oligomer, as a silicone resin, 5.0 g of D-20 (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.) as a curing catalyst, and 5.0 g of Techpolymer MBX-5 (trade name, manufactured by Sekisui Chemical Co., Ltd.), an acrylic light diffusing bead, were placed in a 500 mL beaker and thoroughly stirred with a dissolver to prepare the topcoat coating paints of the Examples.

[0036] In addition, a paint for forming a topcoat coating film of Comparative Example 1 was prepared in the same manner as in the Examples, except that no acrylic light-diffusing beads were used. In addition, a paint for forming a topcoat coating film of Comparative Example 2 was prepared in the same manner as in the Examples, except that 5.0 g of aluminum paste BP-5650 (trade name, manufactured by Toyo Aluminum Co., Ltd.), which is an aluminum pigment, was used instead of the acrylic light-diffusing beads. Furthermore, a paint for forming a topcoat coating film of Comparative Example 3 was prepared in the same manner as in the Examples, except that 5.0 g of stainless steel flake RFA-4000 (trade name, manufactured by Toyo Aluminum Co., Ltd.), which is a stainless steel pigment, was used instead of the acrylic light-diffusing beads.

[0037] Then, on the surfaces of the samples having the four undercoat coating films formed as described above, the topcoat coating paints prepared as described above in Examples and Comparative Examples 1 to 3 were sprayed by air spray method so that the thickness after drying would be approximately 10 μm, and the samples were allowed to dry naturally in the atmosphere for one week, thereby creating painted specimens having a coating film having a multi-layer structure of the undercoat coating films and topcoat coating films of Examples and Comparative Examples 1 to 3.

[0038] The compositions of the paints for forming undercoats and topcoats of Examples and Comparative Examples 1 to 3 thus prepared are summarized in Table 1 below. [Table 1]

[0039] [Measurement of near-infrared reflectance properties] For each of the painted pieces on which the undercoat and topcoat coating films of the Examples and Comparative Examples 1 to 3 were formed as described above, the near-infrared reflected light intensity was measured at incident angles of 90°, 45°, and 20° using an omnidirectional 3D-LiDAR sensor VLP-16 (trade name, manufactured by Velodyne Lider) as the LiDAR sensor as follows. First, the painted pieces 11 of the Examples and Comparative Examples 1 to 3 were placed 5 m away from the front of the LiDAR sensor 10 as shown in Figures 1(a) to (c) and 1(A) to (C). Note that Figures 1(a) to (c) are side views showing the state in which the painted pieces are placed so that the incident angles are 90°, 45°, and 20°, respectively, and Figures 1(A) to (C) are plan views corresponding to Figures 1(a) to (c), respectively.

[0040] The LiDAR sensor 10 irradiated near-infrared light at a predetermined angle of incidence onto each of the painted pieces 11 of the example and comparative examples 1 to 3 to measure the reflected light intensity. In the LiDAR sensor used, the reflected light was displayed as a two-dimensional color image, with red being the part where the reflected light intensity was strong, and changing from green to blue as the reflected light intensity weakened. The signal reception intensity was 30% or less for blue, 50-30% for light blue, 65-50% for green, 80-65% for yellow, and 100-80% for red.

[0041] The results of measuring the reflected light intensity at incident angles of 90°, 45°, and 20° for each of the coated pieces 11 of the example and comparative examples 1 to 3 are shown in Table 2 below. [Table 2]

[0042] The results shown in Table 2 reveal the following. When the incident angle is 90°, the detection result by the LiDAR sensor is red for all the painted pieces of the examples and comparative examples 1 to 3, and the received intensity of the near-infrared reflected light is 100 to 80%. This shows that when the incident angle is around 90°, there is no difference in the reflectivity of near-ultraviolet light depending on whether or not diffusely reflective particles are mixed in the topcoat paint film.

[0043] In contrast, when the incident angle is 45°, the detection result by the LiDAR sensor of the test piece of the embodiment is red, as in the case of an incident angle of 90°, and the received intensity of the near-infrared reflected light is 100 to 80%. However, in the test pieces of Comparative Examples 1 and 2, the detection results by the LiDAR sensor are both a mixture of blue and green, and the received intensity of the near-infrared reflected light is 65 to 30%. Furthermore, in the test piece of Comparative Example 3, the detection result by the LiDAR sensor is blue, and the received intensity of the near-infrared reflected light is 30% or less.

[0044] This shows that in the case of Comparative Example 3, in which a stainless steel pigment was mixed as a diffuse reflection particle in the topcoat coating, the reflectivity of near-infrared light was inferior to that of Comparative Example 1, in which no diffuse reflection particles were mixed, and the detection intensity of near-infrared light by the LiDAR sensor was reduced. Also, in the case of Comparative Example 2, in which an aluminum pigment was mixed as a diffuse reflection particle in the topcoat coating, the diffuse reflection of near-infrared light was equivalent to that of Comparative Example 1, in which no diffuse reflection particles were mixed, and this did not substantially lead to an improvement in the detection intensity of near-infrared light by the LiDAR sensor.

[0045] Furthermore, in the case of an incident angle of 20°, the detection result by the LiDAR sensor in the test piece of the embodiment is red, as in the case of incident angles of 90° and 45°, and the received intensity of the near-infrared reflected light is 100 to 80%. In contrast, all of Comparative Examples 1 to 3 are at the detection limit of the LiDAR sensor. From this, it can be seen that when light diffusing fine particles formed from a polymerizable monomer are added to the topcoat coating film, the near-ultraviolet light reflected by the inorganic near-infrared reflective pigment contained in the undercoat coating film is diffusely reflected by the light diffusing fine particles formed from the polymerizable monomer in the topcoat coating film, so that even if the incident angle of the near-infrared light incident from the LiDAR sensor to the test piece is small, the near-infrared light reflected by the test piece and returning to the LiDAR sensor becomes stronger, and the received intensity becomes higher.

[0046] Therefore, if a multi-layered coating film is used as the coating film formed on the inner wall surface of a tunnel, with a topcoat coating film to which light-diffusing microparticles formed from polymerizable monomers have been added on the surface of an undercoat coating film to which inorganic near-infrared reflective pigments have been added, it is found that even if the angle of incidence of the near-infrared light incident from the LiDAR sensor on the multi-layered coating film is small, the near-infrared light that is diffusely reflected by the multi-layered coating film and returned to the LiDAR sensor can be strengthened. This enables the LiDAR sensor to detect the inner wall surface of the tunnel with high accuracy, and improves the detection accuracy of position information inside the tunnel.

[0047] Furthermore, since the topcoat coating film is made of an inorganic glassy film, the adhesion to the undercoat coating film is extremely good, especially when the resin component of the undercoat coating film is an acrylic silicone resin, and furthermore, exhaust gas and dirt are less likely to adhere to the inner wall of the tunnel, and the coating film also has protection and durability against neutralization, salt damage, frost damage, etc., and is non-flammable. In addition, the coating film of the multi-layer structure of the present invention can be made the same color and gloss as the coating film part of the existing tunnel inner wall surface while maintaining the effect of improving the detection accuracy of position information in the tunnel by the LiDAR sensor, so that it is possible to prevent the general driver from being attracted by the coating film part of the existing tunnel inner wall surface. In addition, even if the coating film of the above-mentioned multi-layer structure is applied to the surface protection of not only the inner wall of the tunnel but also the exposed concrete wall surface, the closed wall surface, various structures, various materials, etc., it is difficult for dirt to adhere due to exhaust gas and rainfall, and furthermore, it is a multi-layer coating film with easy detection by the LiDAR sensor that is environmentally friendly and does not generate harmful substances when disposed of or incinerated. [Explanation of symbols]

[0048] 10. LiDAR sensor 11: Test piece

Claims

1. A coating composition for forming a coating film that is easily detectable by a LiDAR sensor formed on the inner wall surface of a tunnel, A paint for forming an undercoat coating film, in which a near-infrared reflective pigment is blended in a resin component as a binder; a topcoat coating material containing a silicone resin as a binder and light-diffusing fine particles formed from a polymerizable monomer; A coating composition for forming a coating film that is easily detectable by a LiDAR sensor, comprising:

2. The undercoat coating film forming paint is The binder contains an acrylic silicone resin as a resin component, The near-infrared reflective pigment contains 20 to 30% by mass of an inorganic white pigment and 1 to 10% by mass of an inorganic black pigment based on the total amount of the paint for forming the undercoat coating film. The coating composition for forming a coating film, characterized in that it is easily detectable by the LiDAR sensor described in claim 1.

3. The coating material for forming a topcoat coating film is The coating composition for forming a coating film having the ease of detection by the LiDAR sensor described in claim 1, characterized in that the light diffusing microparticles formed from the polymerizable monomer include cross-linked polymethyl methacrylate microparticles, cross-linked polystyrene microparticles, or cross-linked polymethyl methacrylate-styrene copolymer microparticles.

4. A coating film formed using a coating composition for forming a coating film that is easily detectable by the LiDAR sensor according to any one of claims 1 to 3, An undercoat coating film formed using the paint for forming an undercoat coating film; A topcoat coating film formed on the surface of the undercoat coating film using the paint for forming a topcoat coating film; A coating film having a multi-layer structure and being easily detectable by a LiDAR sensor.

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