CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to the specification of Japan Patent Application No. 2020-059261, filed on Mar. 30, 2020, and the specification of Japan Patent Application No. 2020-184041, filed on Nov. 4, 2020 (the entire disclosures of which are incorporated in the present specification by reference).

TECHNICAL FIELD

The present invention relates to a method for forming a multilayer coating film.

BACKGROUND ART

Autonomous driving is attracting attention as a key technology of next-generation automobile technology. To enable autonomous driving, it is necessary to use various sensing technologies, one of which is LIDAR (Light Detection and Ranging). LIDAR can measure the distance to an object by irradiating it with an infrared laser, and detecting the reflected light returned from the object. Thus, LIDAR is useful as a high-precision sensor for detecting medium and long distances.

For example, PTL 1 discloses a light detection and ranging (LIDAR) device, comprising a light source to emit a light beam to scan a scope of orientations associated with a target scanning zone; a first microelectromechanical system (MEMS) mirror configured to receive and redirect the light beam towards the target scanning zone, wherein the first MEMS mirror is configured to tilt in a plurality of directions with respect to the light source to redirect the light beam in a plurality of angles in the plurality of directions; and a light detector to receive the light beam reflected from one or more objects located within the target scanning zone, wherein the first MEMS mirror is arranged to tilt to redirect the light beam at a plurality of angles, and allows the light detector to receive the light beam reflected at a plurality of angles to obtain a multiple angular resolution of the one or more objects.

CITATION LIST

Patent Literature

PTL 1: JP2018-132524A

SUMMARY OF INVENTION

Technical Problem

LIDAR is a sensing technique to measure the distance to an object by irradiating the object with an infrared laser, and detecting the reflected light returned from the object. Thus, the detection sensitivity of LIDAR significantly decreases with an object that does not particularly reflect an infrared laser (e.g., an object with high blackness, such as one with a black color).

However, coating colors with excellent blackness are popular as vehicle coating colors due to the sense of luxury, and are highly demanded. Therefore, there is a demand for coating colors with excellent blackness that can reflect an infrared laser.

Coating is required to impart an excellent appearance to materials, as well as to protect materials; thus, excellent coating film performance, such as high water resistance, is required.

Accordingly, an object of the present invention is to provide a method for forming a multilayer coating film that is capable of forming a multilayer coating film that has excellent blackness, high reflectance of an infrared laser, and excellent coating film performance.

Solution to Problem

A first embodiment of the present invention provides the following method for forming a multilayer coating film, the method comprising

step (1): applying a titanium oxide pigment-containing first colored paint (V) to form a first colored coating film, in which the diffuse reflectance at a wavelength of 905 nm or diffuse reflectance at a wavelength of 1550 nm, or both, is 40% or more,

step (2): applying a second colored paint (W) containing at least one pigment selected from the group consisting of (A1) a perylene black pigment, (A2) a black metal oxide complex pigment, and (A3) two or more pigments selected from the group consisting of blue pigments, red pigments, yellow pigments, and green pigments to the first colored coating film to form a second colored coating film,
step (3): applying a third colored paint (X) containing a carbon black pigment to the second colored coating film to form a third colored coating film,
step (4): applying a clear paint (Y) to the third colored coating film to form a clear coating film, and
step (5): heating the first colored coating film formed in step (1), the second colored coating film formed in step (2), the third colored coating film formed in step (3), and the clear coating film formed in step (4) separately or simultaneously to cure these films,

wherein the multilayer coating film has a lightness) L*(45°) of 3 or less,

the multilayer coating film has a chroma C*(45°) of 1 or less, and

the diffuse reflectance at a wavelength of 905 nm or the diffuse reflectance at a wavelength of 1550 nm of the multilayer coating film, or both, is 10% or more.

Further, a second embodiment of the present invention provides the following method for totaling a multilayer coating film, the method comprising

step (6): applying a titanium oxide pigment-containing first colored paint (V) to form a first colored coating film, in which the diffuse reflectance at a wavelength of 905 nm or diffuse reflectance at a wavelength of 1550 nm, or both, is 40% or more,

step (7): applying a second colored paint (W) containing at least one pigment selected from the group consisting of (A1) a perylene black pigment, (A2) a black metal oxide complex pigment, and (A3) two or more pigments selected from the group consisting of blue pigments, red pigments, yellow pigments, and green pigments to the first colored coating film to form a second colored coating film,
step (8): applying a color clear paint (Z) containing a carbon black pigment to the second colored coating film to form a color clear coating film, and
step (9): heating the first colored coating film formed in step (6), the second colored coating film formed in step (7), and the color clear coating film formed in step (8) separately or simultaneously to cure these films,

wherein the multilayer coating film has a lightness) L*(45°) of 3 or less,

the multilayer coating film has a chroma C*(45°) of 1 or less, and

the diffuse reflectance at a wavelength of 905 nm or the diffuse reflectance at a wavelength of 1550 nm of the multilayer coating film, or both, is 10% or more.

Advantageous Effects of Invention

The method for forming a multilayer coating film according to the present invention is capable of forming a multilayer coating film that has excellent blackness, high reflectance of an infrared laser, and excellent coating film performance, such as water resistance.

