Multi-layer coating method

Abstract

To provide a multiple-layered coating film forming method that can form a multiple-layered coating film that is excellent in jet-blackness, is high in reflectance to infrared laser and can exert high coating performance.SOLUTION: The multiple-layered coating film forming method includes: a step of forming a first colored coating film containing titanium oxide pigment, in which at least either of diffuse reflectance at a wavelength of 905 nm and diffuse reflectance at a wavelength of 1550 nm is 40% or more; a step of forming a second colored coating film containing carbon black pigment (A) as well as at least either (B) of perylene black pigment (B1) and two kinds or more of pigment (B2) selected from a group constituted of blue pigment, red pigment, yellow pigment and green pigment; a step of forming a clear coating film, where brightness L*(45°) of the multiple-layered coating film is 4 or less and colorfulness C*(45°) is 2 or less, and at least either of the diffuse reflectance at the wavelength of 905 nm and the diffuse reflectance at the wavelength of 1550 nm is 10% or more.SELECTED DRAWING: None

Description

[Technical field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims priority based on Japanese Patent Application No. 2020-047664, filed on March 18, 2020, and Japanese Patent Application No. 2020-184042, filed on November 4, 2020, the entire disclosures of which are incorporated herein by reference. The present invention relates to a method for forming a multilayer coating film. [Background technology]

[0002] Autonomous driving is attracting attention as a key technology for next-generation automobiles. To make autonomous driving possible, it is necessary to utilize various sensing technologies, one of which is LIDAR (Light Detection and Ranging). LIDAR can measure the distance to an object by emitting an infrared laser and detecting the reflected light from the object, making it useful as a high-precision sensor for medium to long distances.

[0003] For example, Patent Document 1 discloses a light detection and ranging (LIDAR) device including: a light source that emits a light beam to scan a range of orientations related to a target scanning area; a first microelectromechanical system (MEMS) mirror that is arranged to receive the light beam and redirect it toward the target scanning area, the first MEMS mirror being arranged to tilt in multiple directions relative to the light source to redirect the light beam at multiple angles; and a photodetector that receives a light beam reflected from one or more objects located within the target scanning area, the first MEMS mirror tilting to reflect the light beam emitted by the light source at multiple angles and to have the photodetector receive the light beam reflected at multiple angles to obtain multi-angle resolution of the one or more objects. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-132524 A Summary of the Invention [Problem to be solved by the invention]

[0005] LIDAR is a sensing technology that measures the distance to an object by shining an infrared laser and detecting the reflected light from the object. However, there is a problem with this technology: its detection sensitivity drops significantly for objects that have low infrared laser reflection (for example, objects that are jet black).

[0006] On the other hand, jet-black paint colors are popular for automobiles because they exude a sense of luxury, and so there is a demand for jet-black paint colors that can reflect infrared lasers.

[0007] Furthermore, in addition to providing a beautiful appearance, coatings are also required to protect the substrate, and therefore excellent coating film performance, such as high water resistance, is required.

[0008] Therefore, an object of the present invention is to provide a method for forming a multilayer coating film, which is capable of forming a multilayer coating film that has excellent jet-black color, high reflectance to infrared laser, and can exhibit high coating film performance. [Means for solving the problem]

[0009] The present invention includes subject matter described in the following paragraphs.

[0010] Item 1. Step (1): A step of applying a first colored coating material (X) containing a titanium oxide pigment to form a first colored coating film having at least one of a diffuse reflectance at a wavelength of 905 nm and a diffuse reflectance at a wavelength of 1550 nm of 40% or more; Step (2): A step of applying a second colored coating film onto the first colored coating film, the second colored coating film containing a carbon black pigment (A), and at least one (B) of a perylene black pigment (B1) and two or more pigments (B2) selected from the group consisting of blue pigments, red pigments, yellow pigments, and green pigments, and forming a second colored coating film; Step (3): A step of applying a clear coating (Z) onto the second colored coating film to form a clear coating film; and Step (4): A method for forming a multilayer coating film, comprising a step of heating the first colored coating film formed in step (1), the second colored coating film formed in step (2), and the clear coating film formed in step (3) separately or simultaneously to cure them, The lightness L of the multi-layer coating * (45°) is 4 or less, and Saturation C of the multi-layer coating * (45°) is 2 or less, and A method for forming a multi-layer coating film, characterized in that at least one of the diffuse reflectance at a wavelength of 905 nm and the diffuse reflectance at a wavelength of 1550 nm of the multi-layer coating film is 10% or more.

[0011] Item 2. The method for forming a multilayer coating film according to Item 1, wherein the value obtained by multiplying the cured film thickness (μm) of the second colored coating film by the pigment weight concentration (%) of the carbon black pigment (A) in the second colored coating material (Y) is within the range of 5 to 25.

[0012] Item 3. The method for forming a multilayer coating film according to Item 1 or 2, wherein the pigment weight concentration of the carbon black pigment (A) in the second colored coating material (Y) is within the range of 0.2 to 5%.

[0013] Item 4. The method for forming a multilayer coating film according to any one of Items 1 to 3, wherein the second colored coating material (Y) contains the perylene black pigment (B1), and the pigment weight concentration of the perylene black pigment (B1) is within the range of 3 to 12%.

[0014] Item 5. The method for forming a multilayer coating film according to any one of Items 1 to 3, wherein the second colored coating material (Y) contains two or more pigments (B2) selected from the group consisting of blue pigments, red pigments, yellow pigments, and green pigments, and the total pigment weight concentration of the pigments (B2) is within the range of 3 to 12%. Effect of the Invention

[0015] According to the method for forming a multilayer coating film of the present invention, it is possible to form a multilayer coating film which has excellent jet-blackness, high reflectance to an infrared laser, and excellent coating film properties such as water resistance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Process (1) According to the method of the present invention, first, in step (1), a first colored coating film is formed by applying a first colored coating material (X). The first colored coating material (X) is a coating material that increases the infrared laser reflectance of the multi-layer coating film to be formed, and contains a titanium oxide pigment.

[0017] From the viewpoint of obtaining a multilayer coating film that enhances the hiding power of the base and the reflectance of an infrared laser, the content of the titanium oxide pigment is preferably within a range of 1 to 150 parts by mass, and more preferably within a range of 20 to 120 parts by mass, based on 100 parts by mass of the resin solid content in the first colored coating material (X).

[0018] The first colored coating film has at least one of a diffuse reflectance at a wavelength of 905 nm and a diffuse reflectance at a wavelength of 1550 nm of 40% or more.

[0019] In this specification, the diffuse reflectance is the reflectance not including specular reflection (SCE: Specular Component Excluded) measured using a spectrophotometer equipped with an integrating sphere (Shimadzu Corporation, product name "Solid Spec 3700"), and is the reflectance (relative reflectance) when the reflectance of a standard white board is taken as 100%. In addition, a fluororesin (product name Spectralon, manufactured by Labsphere) is used as the standard white board.

[0020] When at least one of the diffuse reflectance at a wavelength of 905 nm and the diffuse reflectance at a wavelength of 1550 nm of the first colored coating film is 40% or more, a multilayer coating film having high reflectance to infrared laser can be formed.

[0021] From the viewpoint of increasing the reflectance of an infrared laser of the multilayer coating film formed, the first colored coating film has a diffuse reflectance of preferably 45% or more at a wavelength of 905 nm, more preferably 50% or more, and even more preferably 60% or more. The upper limit of the diffuse reflectance of the first colored coating film at a wavelength of 905 nm is not limited, but examples thereof include 99% or less, 95% or less, 90% or less, 85% or less, and 80% or less.

[0022] The diffuse reflectance of the first colored coating film at a wavelength of 1550 nm is preferably 45% or more, more preferably 50% or more, and even more preferably 55% or more, from the viewpoint of increasing the reflectance of an infrared laser of the multilayer coating film formed. The upper limit of the diffuse reflectance of the first colored coating film at a wavelength of 1550 nm is not limited, but examples thereof include 99% or less, 95% or less, 90% or less, 85% or less, and 80% or less.

[0023] In addition, the first colored coating film is L * C * Lightness L in the h color system * (45°) is preferably 55 or more, more preferably 75 or more, and even more preferably 85 or more, from the viewpoint of increasing the reflectance of the infrared laser.

[0024] "L * C * The "L color system" was established by the International Commission on Illumination in 1976 and is also adopted in JIS Z 8781-4 (2013). * a * b * The color system is displayed in polar coordinates, L * The value represents the brightness, C * The value represents the saturation as a distance from the origin, and the h value is L * a * b * a in color system * The red axis is set as 0°, and the hue angle is expressed as the hue angle shifted counterclockwise from this axis.

[0025] Here, the lightness L * (45°) is the brightness L measured when the measurement light is irradiated at an angle of 45° to the axis perpendicular to the measurement surface and the light is received at an angle of 45° from the specular reflection angle to the direction of the measurement light. * It is defined as a value of brightness calculated from the spectral reflectance using a multi-angle spectrophotometer (manufactured by X-rite, product name "MA-68II").

[0026] The first colored paint (X) is preferably a paint that contains, in addition to the titanium oxide pigment, a medium comprising a resin component, water and / or an organic solvent.

[0027] The resin component usually contains a base resin and a curing agent, and known resins and compounds commonly used in the art can be used. Examples of the base resin include acrylic resins, polyester resins, epoxy resins, polyurethane resins, etc. Examples of the curing agent include amino resins, polyisocyanate compounds, blocked polyisocyanate compounds, etc.

[0028] The first colored coating material (X) may be either an aqueous coating material or a solvent-based coating material, but is preferably an aqueous coating material from the viewpoint of reducing the environmental load. When the first colored coating material (X) is an aqueous coating material, the base resin is made water-soluble or water-dispersible by using a resin containing a sufficient amount of hydrophilic groups, such as carboxyl groups, hydroxyl groups, methylol groups, amino groups, sulfonic acid groups, polyoxyethylene groups, etc., most preferably carboxyl groups, to make the base resin water-soluble or water-dispersible, and neutralizing the hydrophilic groups.

[0029] The first colored coating material (X) may further contain, as desired, a color pigment other than the titanium oxide pigment, an extender pigment, a luster pigment, an ultraviolet absorber, a light stabilizer, an antifoaming agent, a thickener, a surface conditioner, and the like.

[0030] Examples of color pigments other than the titanium oxide pigment include carbon black, zinc oxide, molybdenum red, Prussian blue, cobalt blue, azo pigments, phthalocyanine pigments, quinacridone pigments, isoindoline pigments, threne pigments, perylene pigments, dioxazine pigments, diketopyrrolopyrrole pigments, composite metal oxide pigments, etc. Among them, from the viewpoint of the concealing property of the base of the multilayer coating film formed, it is preferable to use carbon black, and from the viewpoint of the brightness of the multilayer coating film formed and the reflectance of infrared laser, it is preferable to use a black composite metal oxide pigment.

[0031] The black composite metal oxide pigment is a calcined black pigment made of a composite of metal oxides of two or more elements, specifically, for example, oxides of Ca-Ti-Mn, Fe-Cr, Mn-Bi, etc.

[0032] In addition, examples of commercially available black composite metal oxide pigments include "Tipake Black SG-101" (Ca-Ti-Mn type, manufactured by Ishihara Sangyo Kaisha), "Black 30C940" (Fe-Cr type, manufactured by Shepherd Chemical Industry Co., Ltd.), "Black 6350" (Fe-Cr type, manufactured by Asahi Sangyo Kaisha), "Black 6301" (Mn-Bi type, manufactured by Asahi Sangyo Kaisha), and "Black 9596" (Fe-Cr type, manufactured by Dainichi Seikagaku Kogyo Co., Ltd.).

[0033] When the first colored coating material (X) contains a colored pigment other than the titanium oxide pigment, the content thereof is preferably 30 parts by mass or less, more preferably within the range of 0.01 to 20 parts by mass, based on 100 parts by mass of the resin solid content in the first colored coating material (X).

[0034] Examples of the extender pigment include clay, kaolin, barium sulfate, barium carbonate, calcium carbonate, talc, silica, and alumina white. Among these, it is preferable to use barium sulfate and / or talc.

[0035] When the first colored coating material (X) contains the above-mentioned extender pigment, the content thereof is preferably 30 parts by mass or less, more preferably within the range of 0.01 to 20 parts by mass, based on 100 parts by mass of the resin solid content in the first colored coating material (X).

[0036] Examples of the luster pigment include aluminum (including vapor-deposited aluminum), copper, zinc, brass, nickel, glass flakes, aluminum oxide, mica, aluminum oxide coated with titanium oxide and / or iron oxide, and mica coated with titanium oxide and / or iron oxide.

[0037] When the first colored coating material (X) contains the above-mentioned luster pigment, the content thereof is preferably 30 parts by mass or less, more preferably within the range of 0.01 to 20 parts by mass, based on 100 parts by mass of the resin solid content in the first colored coating material (X).

[0038] The first colored coating material (X) can be applied according to a conventional method, such as air spray coating, airless spray coating, rotary atomization coating, etc. When applying the first colored coating material (X), electrostatic charge may be applied as necessary, and among these, electrostatic coating by rotary atomization and electrostatic coating by air spray are preferred, with electrostatic coating by rotary atomization being particularly preferred.

[0039] Furthermore, when air spray coating, airless spray coating or rotary atomization coating is performed, the first colored coating material (X) preferably contains water and / or an organic solvent and, if necessary, additives such as a viscosity adjuster and an antifoaming agent to adjust the solids content and viscosity to be suitable for coating.

[0040] The solid content of the first colored coating material (X) is within the range of 10 to 60% by mass, preferably 15 to 55% by mass, and more preferably 20 to 50% by mass. In addition, it is preferable to appropriately adjust the viscosity of the first colored coating material (X) using water and / or an organic solvent so that the viscosity is within a range suitable for coating, usually within the range of 500 to 5000 mPa s when measured at 20°C and 6 rpm using a B-type viscometer.

[0041] The cured film thickness of the first colored coating film is preferably about 5.0 to 40 μm, more preferably about 8.0 to 35 μm, and even more preferably about 10 to 30 μm, from the viewpoint of obtaining a multilayer coating film with high concealing ability for the base and high reflectance for an infrared laser.

[0042] Process (2) According to the method of the present invention, a second colored coating film is then formed by applying a second colored coating (Y) onto the first colored coating film formed in step (1). The second colored coating (Y) contains a carbon black pigment (A) and further contains a perylene black pigment (B1) and at least one of the following pigments (B2): Pigment (B2): Two or more pigments selected from the group consisting of blue pigments, red pigments, yellow pigments, and green pigments. The second colored coating material (Y) has a relatively high transmittance for infrared laser and is capable of forming a coating film having excellent jet black color.

[0043] In the present invention, excellent jet blackness means L * C * Lightness L in the h color system * (45°) and chroma C * (45°) means that both are low.

[0044] Here, saturation C * (45°) is the chroma C measured when the measurement light is irradiated at an angle of 45° to the axis perpendicular to the measurement surface and the light is received at an angle of 45° from the specular reflection angle to the direction of the measurement light. * It is defined as a numerical value of chroma calculated from the spectral reflectance using a multi-angle spectrophotometer (manufactured by X-rite, product name "MA-68II").

[0045] The pigment weight concentration of the carbon black pigment (A) is preferably within the range of 0.2 to 5%, more preferably within the range of 0.25 to 3%, and even more preferably within the range of 0.3 to 2%, from the viewpoint of imparting jet blackness while suppressing a decrease in the infrared laser reflectance of the multilayer coating film to be formed.

[0046] In this specification, the pigment weight concentration is defined as the weight concentration of the pigment based on the total amount of solids in the paint.

[0047] The perylene black pigment (B1) is a pigment that can reduce the brightness while suppressing a decrease in the reflectance of an infrared laser of the multilayer coating film formed.

[0048] Examples of the perylene black pigment (B1) include CI Pigment Black 31 and CI Pigment Black 32. Here, CI stands for Color Index.

[0049] When the second colored coating material (Y) contains a perylene black pigment (B1), from the viewpoint of the brightness and water resistance of the multilayer coating film formed, the pigment weight concentration is preferably within the range of 3 to 12%, and more preferably within the range of 5 to 10%.

[0050] Furthermore, when the second colored coating material (Y) contains a perylene black pigment (B1), from the viewpoints of the infrared laser reflectance, jet-blackness, and water resistance of the multilayer coating film to be formed, the content ratio of the carbon black pigment (A) to the perylene black pigment (B1), in terms of the mass ratio of carbon black pigment (A) / perylene black pigment (B1), is preferably 2 / 98 to 50 / 50, and more preferably 3 / 97 to 30 / 70.

[0051] The two or more pigments (B2) selected from the group consisting of blue pigments, red pigments, yellow pigments and green pigments are a combination of pigments that can reduce the brightness of the second colored coating film formed while suppressing the absorption of infrared laser by the second colored coating film by subtractive color mixing, which is known to those skilled in the art.

[0052] Examples of the blue pigments include CI Pigment Blue 15:1, CI Pigment Blue 15:2, CI Pigment Blue 15:3, CI Pigment Blue 15:4, CI Pigment Blue 15:6, CI Pigment Blue 28, CI Pigment Blue 60, CI Pigment Blue 75, and the like.

[0053] Among the above blue pigments, from the viewpoint of the infrared laser reflectance of the multilayer coating film to be formed, blue pigments having an infrared transmittance of 80% or more at a wavelength of 905 nm and an infrared transmittance of 80% or more at a wavelength of 1550 nm are preferred.

[0054] Examples of blue pigments having an infrared transmittance of 80% or more at a wavelength of 905 nm and an infrared transmittance of 80% or more at a wavelength of 1550 nm include CI Pigment Blue 15:1, CI Pigment Blue 15:2, CI Pigment Blue 15:6, CI Pigment Blue 75, and the like.

[0055] The infrared transmittance at a wavelength of 905 nm and the infrared transmittance at a wavelength of 1,550 nm can be obtained by applying a coating composition containing a coloring pigment onto a polypropylene plate, drying the coating, peeling the coating off from the polypropylene, and measuring the transmittance of the coating using a spectrophotometer equipped with an integrating sphere (manufactured by Shimadzu Corporation, product name "Solid Spec 3700").

[0056] Specifically, 10 parts by mass of one type of color pigment is mixed and stirred per 100 parts by mass of resin solids of a paint made of a hydroxyl group-containing acrylic resin and a melamine resin, and a solvent is added to dilute the solids to about 25%. Next, the resulting paint is applied to a horizontally fixed polypropylene plate using a bar coater so that the film thickness becomes 15 μm as a cured coating film, and after leaving it at room temperature for 10 minutes, it is heated and dried at 100° C. for 60 minutes using a hot air dryer. Next, the resulting coating film is peeled off from the polypropylene plate, and the transmittance of the coating film is measured using a spectrophotometer (manufactured by Shimadzu Corporation, product name "Solid Spec 3700") equipped with an integrating sphere, whereby the transmittance can be obtained.

[0057] When the second colored coating material (Y) contains a blue pigment, the pigment weight concentration is preferably within the range of 0.1 to 6%, and more preferably within the range of 0.5 to 4%.

[0058] Examples of the red pigments include CI Pigment Red 101, CI Pigment Red 122, CI Pigment Red 168, CI Pigment Red 179, CI Pigment Red 202, CI Pigment Red 224, CI Pigment Red 254, CI Pigment Red 255, CI Pigment Red 264, CI Pigment Orange 36, and CI Pigment Violet 19.

[0059] Among the above red pigments, from the viewpoint of the infrared laser reflectance of the multilayer coating film to be formed, red pigments having an infrared transmittance of 80% or more at a wavelength of 905 nm and an infrared transmittance of 80% or more at a wavelength of 1550 nm are preferred.

[0060] Examples of the red pigment having an infrared transmittance of 80% or more at a wavelength of 905 nm and an infrared transmittance of 80% or more at a wavelength of 1550 nm include CI Pigment Red 178, CI Pigment Red 179, CI Pigment Red 202, CI Pigment Red 264, CI Pigment Violet 19, and the like.

[0061] When the second colored coating material (Y) contains a red pigment, the pigment weight concentration is preferably within the range of 0.2 to 10%, and more preferably within the range of 1 to 6%.

[0062] Examples of the yellow pigments include CI Pigment Yellow 42, CI Pigment Yellow 110, CI Pigment Yellow 129, CI Pigment Yellow 138, CI Pigment Yellow 139, CI Pigment Yellow 150, CI Pigment Yellow 151, CI Pigment Yellow 154, CI Pigment Yellow 184, and CI Pigment Yellow 213.

[0063] Among the above yellow pigments, from the viewpoint of the infrared laser reflectance of the multilayer coating film to be formed, yellow pigments having an infrared transmittance of 80% or more at a wavelength of 905 nm and an infrared transmittance of 80% or more at a wavelength of 1550 nm are preferred.

[0064] Examples of yellow pigments having an infrared transmittance of 80% or more at a wavelength of 905 nm and an infrared transmittance of 80% or more at a wavelength of 1550 nm include CI Pigment Yellow 129, CI Pigment Yellow 150, CI Pigment Yellow 213, and the like.

[0065] When the second colored coating material (Y) contains a yellow pigment, the pigment weight concentration is preferably within the range of 0.1 to 6%, and more preferably within the range of 0.5 to 4%.

[0066] Examples of the green pigment include CI Pigment Green 7, CI Pigment Green 26, and CI Pigment Green 36.

[0067] Among the above green pigments, from the viewpoint of the infrared laser reflectance of the multilayer coating film to be formed, green pigments having an infrared transmittance of 80% or more at a wavelength of 905 nm and an infrared transmittance of 80% or more at a wavelength of 1550 nm are preferred.

[0068] Examples of the green pigment having an infrared transmittance of 80% or more at a wavelength of 905 nm and an infrared transmittance of 80% or more at a wavelength of 1550 nm include CI Pigment Green 7 and CI Pigment Green 36.

[0069] When the second colored coating material (Y) contains a green pigment, the pigment weight concentration is preferably within the range of 0.1 to 6%, and more preferably within the range of 0.5 to 4%.

[0070] The two or more pigments (B2) selected from the group consisting of blue pigments, red pigments, yellow pigments and green pigments are preferably three types of blue pigments, red pigments and yellow pigments, from the viewpoint of reducing the brightness while suppressing a decrease in the reflectance of the infrared laser of the multilayer coating film to be formed.

[0071] In addition, the content ratio of the three kinds of blue pigments, red pigments and yellow pigments is preferably 10-40 / 20-80 / 10-40 in terms of the mass ratio of blue pigments / red pigments / yellow pigments, from the viewpoint of reducing the brightness while suppressing a decrease in the reflectance of the infrared laser of the multilayer coating film to be formed.

[0072] When the second colored coating material (Y) contains two or more pigments (B2) selected from the group consisting of blue pigments, red pigments, yellow pigments, and green pigments, the total pigment weight concentration is preferably in the range of 3 to 12%, more preferably in the range of 5 to 10%, from the viewpoint of the brightness and water resistance of the multilayer coating film formed.

[0073] When the second colored coating material (Y) contains two or more pigments (B2) selected from the group consisting of blue pigments, red pigments, yellow pigments, and green pigments, from the viewpoints of the infrared laser reflectance, jet-blackness, and water resistance of the multilayer coating film to be formed, the content ratio of the carbon black pigment (A) to the two or more pigments (B2) selected from the group consisting of blue pigments, red pigments, yellow pigments, and green pigments is preferably 2 / 98 to 50 / 50, and more preferably 3 / 97 to 30 / 70, in terms of the mass ratio of carbon black pigment (A) / two or more pigments (B2) selected from the group consisting of blue pigments, red pigments, yellow pigments, and green pigments.

[0074] The second colored coating material (Y) is preferably a coating material containing, in addition to the carbon black pigment (A), and at least one (B) of the perylene black pigment (B1) and two or more pigments (B2) selected from the group consisting of blue pigments, red pigments, yellow pigments, and green pigments, further containing a medium consisting of a resin component, water and / or an organic solvent.

[0075] The resin component usually contains a base resin and a curing agent, and known resins and compounds commonly used in the art can be used. Examples of the base resin include acrylic resins, polyester resins, epoxy resins, polyurethane resins, etc. Examples of the curing agent include amino resins, polyisocyanate compounds, blocked polyisocyanate compounds, etc.

[0076] The second colored coating material (Y) may be either an aqueous coating material or a solvent-based coating material, but is preferably an aqueous coating material from the viewpoint of reducing environmental load. When the second colored coating material (Y) is an aqueous coating material, the base resin may contain a sufficient amount of hydrophilic groups, such as carboxyl groups, hydroxyl groups, methylol groups, amino groups, sulfonic acid groups, polyoxyethylene groups, etc., most preferably carboxyl groups, to make the resin water-soluble or water-dispersible. In such an embodiment, the base resin can be made water-soluble or water-dispersible by neutralizing the hydrophilic groups.

[0077] The second colored coating material (Y) may further contain, as desired, a coloring pigment other than the above-mentioned carbon black pigment (A), perylene black pigment (B1), and two or more pigments (B2) selected from the group consisting of blue pigments, red pigments, yellow pigments, and green pigments, an extender pigment, a luster pigment, an ultraviolet absorber, a light stabilizer, an antifoaming agent, a thickener, a surface conditioner, etc.

[0078] Examples of coloring pigments other than the carbon black pigment (A), the perylene black pigment (B1), and the two or more pigments (B2) selected from the group consisting of blue pigments, red pigments, yellow pigments, and green pigments include titanium oxide, zinc oxide, and dioxazine pigments.

[0079] When the second colored coating material (Y) contains the above-mentioned carbon black pigment (A), as well as a colored pigment other than the perylene black pigment (B1) and two or more pigments (B2) selected from the group consisting of blue pigments, red pigments, yellow pigments, and green pigments, the pigment weight concentration is preferably 20% or less, and more preferably within the range of 0.01 to 12%.

[0080] Examples of the extender pigment include clay, kaolin, barium sulfate, barium carbonate, calcium carbonate, talc, silica, and alumina white. Among these, it is preferable to use barium sulfate and / or talc.

[0081] When the second colored coating material (Y) contains the above-mentioned extender pigment, the pigment weight concentration is preferably 30% or less, and more preferably within the range of 0.01 to 20%.

[0082] Examples of the luster pigment include aluminum (including vapor-deposited aluminum), copper, zinc, brass, nickel, glass flakes, aluminum oxide, mica, aluminum oxide coated with titanium oxide and / or iron oxide, and mica coated with titanium oxide and / or iron oxide.

[0083] When the second colored coating material (Y) contains the above-mentioned luster pigment, the pigment weight concentration is preferably 20% or less, and more preferably within the range of 0.01 to 12%.

[0084] The second colored coating material (Y) can be applied according to a conventional method, such as air spray coating, airless spray coating, rotary atomization coating, etc. When applying the second colored coating material (Y), electrostatic application may be performed as necessary, and among these, electrostatic coating by rotary atomization and electrostatic coating by air spray are preferred, and electrostatic coating by rotary atomization is particularly preferred.

[0085] Furthermore, when air spray coating, airless spray coating or rotary atomization coating is used, the second colored coating material (Y) preferably contains water and / or an organic solvent and, if necessary, additives such as a viscosity adjuster and an antifoaming agent to adjust the solids content and viscosity to be suitable for coating.

[0086] The solid content of the second colored coating material (Y) is within the range of 10 to 60% by mass, preferably 15 to 55% by mass, and more preferably 20 to 50% by mass. In addition, it is preferable to appropriately adjust the viscosity of the second colored coating material (Y) using water and / or an organic solvent so that the viscosity is within a range suitable for coating, usually within the range of 500 to 5000 mPa s when measured at 20°C and 6 rpm using a B-type viscometer.

[0087] The cured film thickness of the second colored coating film is preferably about 5.0 to 40 μm, more preferably about 8.0 to 35 μm, and even more preferably about 10 to 30 μm, from the viewpoint of imparting jet blackness while suppressing a decrease in the reflectance of the infrared laser of the multilayer coating film to be formed. In the present invention, the second colored coating film may consist of only one layer, or may be composed of multiple layers. However, even when the second colored coating film is composed of multiple layers, the following steps are still included: step (i): applying a first colored paint (v) containing a titanium oxide pigment to form a first colored coating film having at least one of a diffuse reflectance at a wavelength of 905 nm and a diffuse reflectance at a wavelength of 1550 nm of 40% or more; step (ii): a step of applying a second colored coating film onto the first colored coating film, the second colored coating film (w) containing at least one pigment selected from the group consisting of (a1) a perylene black pigment, (a2) a black composite metal oxide pigment, and (a3) ​​two or more pigments selected from the group consisting of blue pigments, red pigments, yellow pigments, and green pigments, to form a second colored coating film; Step (iii): A step of applying a third colored paint (x) containing a carbon black pigment onto the second colored coating film to form a third colored coating film; Step (iv): A step of applying a clear coating (y) onto the third colored coating film to form a clear coating film; and Step (v): A method for forming a multilayer coating film, comprising a step of heating and curing the first colored coating film formed in step (i), the second colored coating film formed in step (ii), the third colored coating film formed in step (iii), and the clear coating film formed in step (iv) separately or simultaneously, The lightness L*(45 °) of the multilayer coating film is 3 or less, and The chroma C*(45 °) of the multilayer coating film is 1 or less, and The present invention does not include a method for forming a multilayer coating film, characterized in that at least one of the diffuse reflectance at a wavelength of 905 nm and the diffuse reflectance at a wavelength of 1550 nm of the multilayer coating film is 10% or more. As described above, the second colored coating film is formed by coating with a second colored paint (Y). As described above, the second colored paint (Y) contains a carbon black pigment (A), a perylene black pigment (B1), and at least one (B) of two or more pigments (B2) selected from the group consisting of blue pigments, red pigments, yellow pigments, and green pigments. Therefore, when the second colored coating film is composed of multiple layers, each layer constituting the multiple layers contains a carbon black pigment (A), and at least one (B) of two or more pigments (B2) selected from the group consisting of perylene black pigment (B1), blue pigments, red pigments, yellow pigments, and green pigments.

[0088] In addition, from the viewpoint of imparting jet blackness while suppressing a decrease in the reflectance of an infrared laser of the multilayer coating film formed, the value obtained by multiplying the cured film thickness (μm) of the second colored coating film and the pigment weight concentration (%) of the carbon black pigment (A) in the second colored paint (Y) is preferably within the range of 5 to 25, and more preferably within the range of 7 to 15.

[0089] Process (3) According to the method for forming a multilayer coating film of the present invention, a clear coating film is formed by coating a clear coating film (Z) on the second colored coating film obtained by coating the second colored coating film (Y) as described above.

[0090] The clear paint (Z) used in the method of the present invention can be any known clear paint without any restrictions.Specific examples include liquid or powder clear paints that contain a resin component consisting of a base resin and a hardener as essential components, and further contain paint additives, solvents such as water or organic solvents, etc., as necessary, and form a colorless or colored transparent coating film.

[0091] Examples of the base resin include resins containing crosslinkable functional groups such as hydroxyl groups, carboxyl groups, silanol groups, epoxy groups, etc., such as acrylic resins, polyester resins, alkyd resins, fluororesins, urethane resins, and silicon-containing resins. Examples of the curing agent include compounds or resins having functional groups capable of reacting with the functional groups of the base resin, such as melamine resins, urea resins, polyisocyanate compounds, blocked polyisocyanate compounds, epoxy compounds or resins, carboxyl group-containing compounds or resins, acid anhydrides, and alkoxysilyl group-containing compounds or resins.

[0092] The ratio of the base resin and the curing agent in the resin component is not particularly limited, but in general, the curing agent can be used within the range of 10 to 100 mass %, preferably 20 to 80 mass %, and more preferably 30 to 60 mass %, based on the total amount of solid content of the base resin.

[0093] The clear coating (Z) may contain, as necessary, water, solvents such as organic solvents, curing catalysts, antifoaming agents, ultraviolet absorbers, rheology control agents, anti-settling agents and other coating additives.

[0094] In the clear coating (Z), a coloring pigment can be appropriately used within a range that does not impair the transparency of the coating film. As the coloring pigment, a pigment known per se for ink or coating can be used alone or in combination of two or more kinds. The blending amount varies depending on the type of coloring pigment used, but can be usually 30 mass% or less, preferably 0.05 to 20 mass%, more preferably 0.1 to 10 mass% based on the total solid content of the resin component in the clear coating.

[0095] The clear coating material (Z) can be applied by electrostatic coating, air spray, airless spray or the like, and the thickness of the clear coating film is about 10 to 60 μm, more preferably about 15 to 50 μm, and even more preferably about 20 to 40 μm, based on the cured coating film.

[0096] The solid content of the clear coating material (Z) is within the range of 10 to 65% by mass, preferably 15 to 55% by mass, and more preferably 20 to 50% by mass. It is also preferable to appropriately adjust the viscosity of the clear coating material (Z) using water and / or an organic solvent so that it is within a range suitable for coating, usually within the range of about 15 to 60 seconds, particularly about 20 to 50 seconds, at 20°C using a Ford Cup No. 4 viscometer.

[0097] Process (4) According to the method for forming a multilayer coating film of the present invention, the first colored coating film formed in step (1), the second colored coating film formed in step (2), and the clear coating film formed in step (3) are cured by heating separately or simultaneously.

[0098] In particular, from the viewpoint of energy saving and the like, it is preferable to heat the first colored coating film, the second colored coating film and the clear coating film simultaneously.

[0099] Heating can be performed by known means, for example, drying ovens such as hot air ovens, electric ovens, and infrared induction heating ovens. The heating temperature is preferably within the range of 70 to 150° C., more preferably 80 to 140° C. The heating time is not particularly limited, but is preferably within the range of 10 to 40 minutes, more preferably 20 to 30 minutes.

[0100] Base material There is no particular restriction on the substrate to which the multilayer coating film forming method of the present invention can be applied, and examples thereof include members made of metals such as iron, zinc, aluminum, magnesium, etc.; members made of alloys of these metals; members plated or vapor-deposited with these metals; members made of glass, plastics, foams of various materials, etc., and among these, steel and plastic materials constituting automobile bodies are suitable, and steel is particularly suitable. These members can be subjected to appropriate treatments such as degreasing and surface treatment as necessary.

[0101] Furthermore, the above-mentioned member can also be used as a substrate after forming an undercoat film and / or an intermediate coat film, and this is generally preferred.

[0102] The undercoat coating film is applied to the surface of a component to conceal the surface of the component or to impart anticorrosive and antirust properties to the component, and can be formed by applying and curing an undercoat paint. This undercoat paint is not particularly limited, and known paints such as electrodeposition paints and solvent-based primers can be used.

[0103] The intermediate coating film is applied to the base in order to conceal the base such as the surface of a member and the undercoat coating film, to improve adhesion between the base and the topcoat coating film, to impart chipping resistance to the coating film, etc., and can be formed by applying an intermediate coating paint to the surface of the base such as the surface of a member and the undercoat coating film and curing it. This intermediate coating paint is not particularly limited, and any known intermediate coating paint can be used. For example, an organic solvent-based or water-based intermediate coating paint containing a thermosetting resin composition and a color pigment can be preferably used.

[0104] In the method for forming a multilayer coating film of the present invention, when a member on which an undercoat coating film and / or an intermediate coating film has been formed is used as the substrate, the undercoat coating film and / or the intermediate coating film may be heated and cured in advance, and then the first colored paint (X) may be applied in step (1). Alternatively, the first colored paint (X) may be applied to the undercoat coating film and / or the intermediate coating film in an uncured state.

[0105] Multi-layer coating According to the method for forming a multilayer coating film of the present invention, Step (1): A step of applying a first colored coating material (X) containing a titanium oxide pigment to form a first colored coating film having at least one of a diffuse reflectance at a wavelength of 905 nm and a diffuse reflectance at a wavelength of 1550 nm of 40% or more; Step (2): A step of applying a second colored coating film onto the first colored coating film, the second colored coating film containing a carbon black pigment (A), and at least one (B) of a perylene black pigment (B1) and two or more pigments (B2) selected from the group consisting of blue pigments, red pigments, yellow pigments, and green pigments, and forming a second colored coating film; Step (3): A step of applying a clear coating (Z) onto the second colored coating film to form a clear coating film; and Step (4): The first colored coating film formed in step (1), the second colored coating film formed in step (2), and the clear coating film formed in step (3) are heated separately or simultaneously to harden them, thereby forming a multi-layer coating film; The lightness L of the multi-layer coating *(45°) is 4 or less, and Saturation C of the multi-layer coating * (45°) is 2 or less, and By having at least one of the diffuse reflectance at a wavelength of 905 nm and the diffuse reflectance at a wavelength of 1550 nm of 10% or more, it is possible to form a multilayer coating film that has excellent jet-black color, high infrared laser reflectance, and excellent coating performance such as water resistance.

[0106] The lightness L of the above multi-layer coating * (45°) is 4 or less, and chroma is C * By making the (45°) angle θ equal to or less than 2, a multi-layer coating film having excellent jet-black properties can be formed. In particular, from the viewpoint of forming a multi-layer coating film having excellent jet-black properties, the lightness L * (45°) is preferably 3.5 or less, and more preferably 3 or less. In a typical embodiment of the present invention, the lightness L * (45°) of 4 or less indicates that the chroma is 4.0 or less, and 3 or less indicates that the chroma is 3.0 or less. In a typical embodiment of the present invention, the chroma C * (45°) is 2 or less means 2.0 or less. * The lower limit of (45°) is not limited, but may be, for example, 0.1 or more, 0.2 or more, 0.3 or more, 0.5 or more, etc. * From the viewpoint of forming a multi-layer coating film having excellent jet blackness, the angle (45°) is preferably 1.5 or less, more preferably 1.3 or less, and even more preferably 1.0 or less. * The lower limit of (45°) is not limited, but examples include 0.01 or more, 0.02 or more, 0.03 or more, and 0.05 or more.

[0107] Furthermore, by having at least one of the diffuse reflectance at a wavelength of 905 nm and the diffuse reflectance at a wavelength of 1550 nm of 10% or more, a multilayer coating film having excellent reflectance to infrared laser can be formed.

[0108] In particular, the diffuse reflectance of the multilayer coating film at a wavelength of 905 nm is preferably 11% or more, more preferably 12% or more, from the viewpoint of forming a multilayer coating film with excellent infrared laser reflectance. The upper limit of the diffuse reflectance of the multilayer coating film at a wavelength of 905 nm is not limited, but examples thereof include 90% or less, 80% or less, 70% or less, 60% or less, and 50% or less.

[0109] In addition, the diffuse reflectance of the multilayer coating film at a wavelength of 1550 nm is preferably 12% or more, more preferably 14% or more, from the viewpoint of forming a multilayer coating film with excellent infrared laser reflectance. The upper limit of the diffuse reflectance of the multilayer coating film at a wavelength of 1550 nm is not limited, but examples thereof include 90% or less, 80% or less, 70% or less, 60% or less, and 50% or less.

[0110] From the viewpoint of forming a multilayer coating film that has excellent jet-blackness, high infrared laser reflectance, and excellent coating performance such as water resistance, the multilayer coating film forming method of the present invention is preferably the following multilayer coating film forming method (a) or (b).

[0111] Multi-layer coating method (a): Step (1a): A step of applying a first colored coating material (X) containing a titanium oxide pigment to form a first colored coating film having a diffuse reflectance of 40% or more at a wavelength of 905 nm; Step (2a): A step of applying a second colored coating film onto the first colored coating film, the second colored coating film containing a carbon black pigment (A), and at least one (B) of a perylene black pigment (B1) and two or more pigments (B2) selected from the group consisting of blue pigments, red pigments, yellow pigments, and green pigments; Step (3a): A step of applying a clear coating (Z) onto the second colored coating film to form a clear coating film; and Step (4a): The first colored coating film formed in step (1a), the second colored coating film formed in step (2a), and the clear coating film formed in step (3a) are heated separately or simultaneously to harden them, thereby forming a multi-layer coating film; The lightness L of the multi-layer coating * (45°) is 4 or less, and Saturation C of the multi-layer coating * (45°) is 2 or less, and The method for forming a multi-layer coating film, wherein the multi-layer coating film has a diffuse reflectance of 10% or more at a wavelength of 905 nm.

[0112] Multi-layer coating method (b): Step (1b): A step of applying a first colored coating material (X) containing a titanium oxide pigment to form a first colored coating film having a diffuse reflectance of 40% or more at a wavelength of 1550 nm; step (2b): a step of applying a second colored coating film onto the first colored coating film, the second colored coating film being formed by applying a second colored coating (Y) containing a carbon black pigment (A), and at least one (B) of a perylene black pigment (B1) and two or more pigments (B2) selected from the group consisting of blue pigments, red pigments, yellow pigments, and green pigments; Step (3b): A step of applying a clear coating (Z) onto the second colored coating film to form a clear coating film; and Step (4b): The first colored coating film formed in step (1b), the second colored coating film formed in step (2b), and the clear coating film formed in step (3b) are heated separately or simultaneously to harden them, thereby forming a multi-layer coating film; The lightness L of the multi-layer coating * (45°) is 4 or less, and Saturation C of the multi-layer coating * (45°) is 2 or less, and The method for forming a multi-layer coating film, wherein the multi-layer coating film has a diffuse reflectance of 10% or more at a wavelength of 1550 nm.

[0113] Thus, the method for forming a multi-layer coating film of the present invention can be suitably used for forming a multi-layer coating film on various industrial products, particularly on the outer panels of automobile bodies. EXAMPLES

[0114] The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited to these examples. Note that "parts" and "%" are all based on mass, and the film thickness is based on the cured coating film.

[0115] [1] Preparation of substrate A degreased and zinc phosphate-treated steel plate (JIS G 3141, size 400 mm x 300 mm x 0.8 mm) was electrocoated with cationic electrodeposition paint "Elecron GT-10" (product name: manufactured by Kansai Paint Co., Ltd., epoxy resin polyamine cationic resin with a blocked polyisocyanate compound as a curing agent) to a film thickness of 20 μm based on the cured coating, and heated at 170°C for 20 minutes to crosslink and cure, forming an electrodeposition coating film.

[0116] [2] Preparation of paint Preparation of Hydroxyl-Containing Acrylic Resin Emulsion (a) Manufacturing Example 1 In a reaction vessel equipped with a thermometer, a thermostat, a stirring device, a reflux condenser and a dropping device, 70.7 parts of deionized water and 0.52 parts of "Aqualon KH-10" (trade name, Daiichi Kogyo Seiyaku Co., Ltd., emulsifier, active ingredient 97%) were charged, and the mixture was stirred and mixed in a nitrogen stream and heated to 80°C. Next, 1% of the total amount of the monomer emulsion described below and 5 parts of a 6% aqueous solution of ammonium persulfate were introduced into the reaction vessel and kept at 80°C for 15 minutes. Thereafter, the remaining monomer emulsion was dropped into the reaction vessel kept at the same temperature over 3 hours, and after the completion of the dropping, the mixture was aged for 1 hour, and then cooled to 30°C while gradually adding 40 parts of a 5% aqueous solution of 2-(dimethylamino)ethanol to the reaction vessel, and the mixture was discharged while filtering through a 100-mesh nylon cloth, to obtain a hydroxyl-containing acrylic resin emulsion (a) with a solid content concentration of 45%. The resulting hydroxyl-containing acrylic resin had a hydroxyl value of 43 mgKOH / g and an acid value of 12 mgKOH / g.

[0117] Monomer emulsion: 50 parts of deionized water, 10 parts of styrene, 40 parts of methyl methacrylate, 35 parts of ethyl acrylate, 3.5 parts of n-butyl methacrylate, 10 parts of 2-hydroxyethyl methacrylate, 1.5 parts of acrylic acid, 1.0 part of "Aqualon KH-10" and 0.03 parts of ammonium persulfate were mixed and stirred to obtain a monomer emulsion.

[0118] Preparation of Hydroxyl-Containing Polyester Resin Solution (b) Manufacturing Example 2 In a reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser and a water separator, 174 parts of trimethylolpropane, 327 parts of neopentyl glycol, 352 parts of adipic acid, 109 parts of isophthalic acid and 101 parts of 1,2-cyclohexanedicarboxylic anhydride were charged, and the temperature was raised from 160 ° C to 230 ° C over 3 hours, and the generated condensed water was distilled off by a water separator while maintaining the temperature at 230 ° C, and the reaction was continued until the acid value was 3 mg KOH / g or less. 59 parts of trimellitic anhydride was added to this reaction product, and an addition reaction was carried out at 170 ° C for 30 minutes, and then the mixture was cooled to 50 ° C or less, and 2- (dimethylamino) ethanol was added in an equivalent amount to the acid group to neutralize it, and deionized water was gradually added to obtain a hydroxyl group-containing polyester resin solution (b) with a solid content concentration of 45%. The resulting hydroxyl-containing polyester resin had a hydroxyl value of 128 mgKOH / g, an acid value of 35 mgKOH / g and a weight average molecular weight of 13,000.

[0119] Manufacturing of pigment dispersion pastes (P-1) to (P-5) Production Example 3 56 parts (25 parts solids) of the hydroxyl-containing polyester resin solution (b) obtained in Production Example 2, 100 parts of "Tipake UT-771" (trade name, rutile-type titanium dioxide pigment, manufactured by Ishihara Sangyo Kaisha), 0.03 parts of "Carbon MA-100" (trade name, carbon black pigment, manufactured by Mitsubishi Chemical Corporation), and 5 parts of deionized water were mixed and adjusted to pH 8.0 with 2-(dimethylamino)ethanol. The resulting mixture was then placed in a wide-mouth glass bottle, glass beads with a diameter of about 1.3 mm were added as a dispersion medium, the bottle was sealed, and the mixture was dispersed for 30 minutes using a paint shaker to obtain a pigment dispersion paste (P-1).

[0120] Manufacturing Examples 4 to 7 Each pigment dispersion paste (P-2) to (P-5) was obtained in the same manner as in Production Example 3, except that the color pigment composition was as shown in the following Table 1. The color pigment composition shown in Table 1 is based on the solid content mass of each component.

[0121] [Table 1]

[0122] UT-771 (Note 1): Rutile titanium dioxide pigment, product name, "Tipaque UT-771", manufactured by Ishihara Sangyo Kaisha, Ltd. MA-100 (Note 2): Carbon black pigment, trade name, "Carbon MA-100", manufactured by Mitsubishi Chemical Corporation. SG-101 (Note 3): Composite metal oxide pigment, CaO·TiO 2 MnO 2 The product name is "Typique Black SG-101", manufactured by Ishihara Sangyo Kaisha.

[0123] Manufacture of first colored paint (X-1) to (X-5) Production Example 8 161.03 parts of the pigment dispersion paste (P-1) obtained in Production Example 3, 44.4 parts (20 parts solids) of the hydroxyl-containing acrylic resin emulsion (a) obtained in Production Example 1, 71.4 parts (25 parts solids) of "U-coat UX-8100" (product name, urethane emulsion, manufactured by Sanyo Chemical Industries, 35% solids), and 37.5 parts (30 parts solids) of "Cymel 325" (product name, melamine resin, manufactured by Nippon Cytec Industries, 80% solids) were uniformly mixed. Next, "UH-752" (product name, manufactured by ADEKA, thickener), 2-(dimethylamino)ethanol, and deionized water were added to the resulting mixture to obtain a first colored paint (X-1) having a pH of 8.0, a paint solids content of 25%, and a viscosity of 3000 mPa·s when measured using a B-type viscometer at 20 ° C. and a rotation speed of 6 rpm.

[0124] Manufacturing Examples 9-12 Except for using the formulations shown in Table 2 below, the same procedure as in Production Example 8 was repeated to obtain first colored coatings (X-2) to (X-5) each having a viscosity of 3000 mPa·s when measured at 20°C and 6 rpm using a B-type viscometer.

[0125] Evaluation of the first colored coating Using the first colored paints (X-1) to (X-5) obtained above, the diffuse reflectance at a wavelength of 905 nm and the diffuse reflectance at a wavelength of 1550 nm of the first colored coating film were measured using a "Solid Spec 3700" (product name, manufactured by Shimadzu Corporation) as a spectrophotometer, and a fluororesin (product name, Spectralon, manufactured by Labsphere) as a standard white board for measuring the relative reflectance excluding specular reflection (SCE: Specular Component Excluded). In addition, the lightness L of the first colored coating film * (45°) was evaluated using "MA-68II" (trade name, manufactured by X-rite). The first colored coating film was obtained by applying any one of the first colored paints (X-1) to (X-5) to the substrate prepared in [1] above using a mini-bell type rotary electrostatic coating machine under conditions of a booth temperature of 23°C and humidity of 68% so as to give a film thickness of 30 μm as a cured coating film, leaving it at room temperature for 3 minutes, and heating it at 140°C for 30 minutes in a hot air circulation drying oven. The evaluation results are also shown in Table 2.

[0126] [Table 2]

[0127] Preparation of hydroxyl-containing acrylic resin emulsion (c) Manufacturing Example 13 In a reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser, and a dropping device, 130 parts of deionized water and 0.52 parts of "Aqualon KH-10" were charged, and the mixture was stirred and mixed in a nitrogen stream and heated to 80°C. Next, 1% of the total amount of the monomer emulsion (1) described below and 5.3 parts of a 6% aqueous solution of ammonium persulfate were introduced into the reaction vessel and kept at 80°C for 15 minutes. After that, the remaining monomer emulsion (1) was dropped into the reaction vessel kept at the same temperature over 3 hours, and after the end of the dropping, the mixture was aged for 1 hour. After that, the monomer emulsion (2) described below was dropped over 1 hour, and after aging for 1 hour, the mixture was cooled to 30°C while gradually adding 40 parts of a 5% aqueous solution of dimethylethanolamine to the reaction vessel, and the mixture was discharged while filtering through a 100-mesh nylon cloth, to obtain a hydroxyl-containing acrylic resin emulsion (c) with a solid concentration of 30%. The resulting hydroxyl-containing acrylic resin had a hydroxyl value of 25 mgKOH / g and an acid value of 33 mgKOH / g.

[0128] Monomer emulsion (1): 42 parts of deionized water, 0.72 parts of "Aqualon KH-10", 2.1 parts of methylenebisacrylamide, 2.8 parts of styrene, 16.1 parts of methyl methacrylate, 28 parts of ethyl acrylate, and 21 parts of n-butyl acrylate were mixed and stirred to obtain a monomer emulsion (1).

[0129] Monomer emulsion (2): 18 parts of deionized water, 0.31 parts of "Aqualon KH-10", 0.03 parts of ammonium persulfate, 5.1 parts of methacrylic acid, 5.1 parts of 2-hydroxyethyl acrylate, 3 parts of styrene, 6 parts of methyl methacrylate, 1.8 parts of ethyl acrylate, and 9 parts of n-butyl acrylate were mixed and stirred to obtain a monomer emulsion (2).

[0130] Preparation of Hydroxyl-Containing Polyester Resin Solution (d) Manufacturing Example 14 In a reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser and a water separator, 109 parts of trimethylolpropane, 141 parts of 1,6-hexanediol, 126 parts of hexahydrophthalic anhydride and 120 parts of adipic acid were charged and heated, and the temperature was raised from 160°C to 230°C over 3 hours, and then condensation reaction was carried out at 230°C for 4 hours. Next, in order to add a carboxyl group to the obtained condensation reaction product, 38.3 parts of trimellitic anhydride were further added, and the reaction was carried out at 170°C for 30 minutes, and then diluted with 2-ethyl-1-hexanol to obtain a hydroxyl group-containing polyester resin solution (d) with a solid content concentration of 70%. The obtained hydroxyl group-containing polyester resin had a hydroxyl value of 150 mgKOH / g, an acid value of 46 mgKOH / g and a weight average molecular weight of 6,400.

[0131] Manufacturing of pigment dispersion pastes (P-6) to (P-24) Manufacturing Example 15 35.7 parts (25 parts solids) of the hydroxyl-containing polyester resin solution (d) obtained in Production Example 14, 0.5 parts of "RAVEN 5000 ULTRA III BEADS" (trade name, carbon black pigment, manufactured by COLUMBIAN CARBON CO.), 6 parts of "Paliogen Black L0086" (trade name, perylene black pigment, CI Pigment Black 32, manufactured by BASF) and 5 parts of deionized water were mixed and adjusted to pH 8.0 with 2-(dimethylamino)ethanol. Next, the resulting mixture was placed in a wide-mouth glass bottle, glass beads with a diameter of about 1.3 mm were added as a dispersion medium, and the bottle was sealed. The mixture was dispersed for 30 minutes using a paint shaker to obtain a pigment dispersion paste (P-6).

[0132] Manufacturing Examples 16-33 Each pigment dispersion paste (P-7) to (P-24) was obtained in the same manner as in Production Example 13, except that the color pigment composition was as shown in the following Table 3. The color pigment composition shown in Table 3 is based on the solid content mass of each component.

[0133] [Table 3]

[0134] [Table 4]

[0135] R5000 (Note 4): Carbon black pigment, product name, "RAVEN 5000 ULTRA III BEADS", manufactured by COLUMBIA CARBON CO., L0086 (Note 5): Perylene black pigment, CI Pigment Black 32, trade name, "Paliogen Black L0086", manufactured by BASF, 5206M (Note 6): Blue pigment, CIPigment Blue 15:1, product name, "CYANINE BLUE 5206M", manufactured by Dainichiseika Kogyo Co., Ltd. R6438 (Note 7): Red pigment, CI Pigment Red 179, trade name, "MAROON 179 229-6438", manufactured by Sun Chemical Co., Y5688 (Note 8): Yellow pigment, CI Pigment Yellow 150, trade name, "BAYFAST YELLOW Y-5688", manufactured by LANXESS, L8730 (Note 9): Green pigment, CI Pigment Green 7, trade name, "HELIOGEN GREEN L8730", manufactured by BASF.

[0136] Evaluation of blue, red, yellow and green pigments The blue pigment, red pigment, yellow pigment and green pigment used above were evaluated for infrared transmittance at a wavelength of 905 nm and infrared transmittance at a wavelength of 1550 nm by the following method.

[0137] Infrared transmittance at wavelengths of 905 nm and 1550 nm A coating material consisting of 70 parts of the hydroxyl-containing acrylic resin solution described below and 30 parts of "Cymel 350" (trade name, melamine resin, manufactured by Allnex Japan Co., Ltd.) was mixed with 10 parts of the pigment to be measured per 100 parts of resin solids, and the mixture was stirred and mixed, and deionized water was added to dilute the solids to about 25%. The coating material obtained was then applied to a horizontally fixed polypropylene plate using a bar coater so that the film thickness of the cured coating film was 15 μm, and the plate was left at room temperature for 10 minutes, and then heated and dried at 100 ° C. for 60 minutes using a hot air dryer. The coating film obtained was then peeled off from the polypropylene plate, and the transmittance of the coating film was measured and evaluated using a spectrophotometer equipped with an integrating sphere (manufactured by Shimadzu Corporation, trade name, "Solid Spec 3700"). The evaluation results are shown in Table 4.

[0138] Hydroxyl-containing acrylic resin solution: 35 parts of propylene glycol monopropyl ether was charged into a reaction vessel equipped with a thermometer, a thermostat, a stirring device, a reflux condenser, a nitrogen inlet tube and a dropping device, and the temperature was raised to 85°C. Then, a mixture of 30 parts of methyl methacrylate, 20 parts of 2-ethylhexyl acrylate, 29 parts of n-butyl acrylate, 15 parts of 2-hydroxyethyl acrylate, 6 parts of acrylic acid, 15 parts of propylene glycol monopropyl ether and 2.3 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) was added dropwise over 4 hours, and the mixture was aged for 1 hour after the end of the dropwise addition. Then, a mixture of 10 parts of propylene glycol monopropyl ether and 1 part of 2,2'-azobis(2,4-dimethylvaleronitrile) was added dropwise over 1 hour, and the mixture was aged for 1 hour after the end of the dropwise addition. 7.4 parts of diethanolamine were added to obtain a hydroxyl-containing acrylic resin solution with a solid content of 55%. The resulting hydroxyl-containing acrylic resin solution had an acid value of 47 mgKOH / g, a hydroxyl value of 72 mgKOH / g, and a weight average molecular weight of 58,000.

[0139] [Table 5]

[0140] Manufacture of second colored paint (Y-1) to (Y-19) Manufacturing Example 34 47.2 parts of the pigment dispersion paste (P-6) obtained in Production Example 15, 83.3 parts (25 parts solids) of the hydroxyl-containing acrylic resin emulsion (c) obtained in Production Example 13, 57.1 parts (20 parts solids) of "U-coat UX-8100" (product name, urethane emulsion, manufactured by Sanyo Chemical Industries, 35% solids), and 37.5 parts (30 parts solids) of "Cymel 325" (product name, melamine resin, manufactured by Allnex, 80% solids) were uniformly mixed. Next, "UH-752" (product name, manufactured by ADEKA, thickener), 2-(dimethylamino)ethanol, and deionized water were added to the resulting mixture to obtain a second colored paint (Y-1) having a pH of 8.0, a paint solids content of 25%, and a viscosity of 3000 mPa·s when measured using a B-type viscometer at 20°C and a rotation speed of 6 rpm.

[0141] Manufacturing Examples 35-52 First colored coatings (Y-2) to (Y-19) each having a viscosity of 3000 mPa s when measured at 20°C and 6 rpm using a B-type viscometer were obtained in the same manner as in Production Example 34, except that the blending compositions were as shown in Table 5 below. Note that the numbers in parentheses for the resin components in the table indicate the solid content.

[0142] [Table 6]

[0143] [Table 7]

[0144] [Table 8]

[0145] [3] Creating test panels Creating test panels Example 1 (Painting of the first colored paint (X)) The first colored coating material (X-1) produced in [2] above was applied onto the substrate prepared in [1] above using a mini-bell type rotary electrostatic coating machine under conditions of a booth temperature of 23°C and a humidity of 68% so as to give a cured coating film with a thickness of 30 μm, and the coating was left to stand at room temperature for 3 minutes to obtain an uncured first colored coating film.

[0146] (Painting of the second colored paint (Y)) The second colored paint (Y-1) prepared in [2] above was applied onto the uncured first colored coating film using a mini-bell type rotary electrostatic coating machine under conditions of a booth temperature of 23°C and a humidity of 68% so as to give a cured coating film with a thickness of 15 μm. The coating was then left at room temperature for 3 minutes and preheated at 80°C for 3 minutes to obtain an uncured second colored coating film.

[0147] (Clear paint (Z) painting) A clear paint (Z) ("Magicron KINO-1210", product name, manufactured by Kansai Paint Co., Ltd., acrylic resin-based acid / epoxy curing solvent-type topcoat clear paint) was applied onto the uncured second colored coating film using a mini bell-type rotary electrostatic coating machine at a booth temperature of 23°C and humidity of 68% so that the cured coating film would be 35 μm thick. The coating was then left at room temperature for 7 minutes and then heated at 140°C for 30 minutes in a hot air circulating drying oven to simultaneously dry and cure the multi-layer coating film consisting of the first colored coating film, the second colored coating film and the clear coating film, to produce a test panel.

[0148] Examples 2 to 13, Comparative Examples 1 to 10 Test panels were obtained in the same manner as in Example 1, except that the paint and film thicknesses shown in Table 6 were used.

[0149] Coating evaluation The coating film of each test plate obtained as described above was evaluated by the following methods, and the results are shown in Table 6.

[0150] Lightness L * (45°) For each test panel, the brightness L was measured using "MA-68II" (product name, manufactured by X-Rite Co., Ltd.) * (45°) was measured.

[0151] Saturation C * (45°) For each test plate, the chroma C was measured using "MA-68II" (product name, manufactured by X-Rite Co., Ltd.). * (45°) was measured.

[0152] Diffuse reflectance at wavelengths of 905 nm and 1550 nm (measurement of infrared laser reflectance) The reflectance excluding specular component (SCE) of each test plate was measured using "Solid Spec 3700" (product name, manufactured by Shimadzu Corporation).

[0153] Water-resistant adhesion: Each test panel was immersed in 40°C warm water for 240 hours, and immediately after being pulled out and the surface moisture wiped off, 100 2mm x 2mm cross-hatched patterns were made on the coating film in accordance with JIS K 5600-5-6 (1990), adhesive tape was applied to the surface, and the tape was quickly peeled off, after which the number of cross-hatched coating films remaining on the coating film was evaluated. ◎ and ○ indicate passing.

[0154] ◎: Remaining number / total number = 100 / 100 with no chipped edges ○: Number of remaining pieces / total number = 100 pieces / 100 pieces with chipped edges △: Remaining number / Total number=99~90 / 100 ×: Remaining number / total number = 89 or less / 100.

[0155] [Table 9]

[0156] [Table 10]

Claims

1. Step (1): A step of applying a first colored coating material (X) containing a titanium oxide pigment to form a first colored coating film having a diffuse reflectance of 40% or more at least at a wavelength of 905 nm and a diffuse reflectance of 1,550 nm; Step (2): A step of coating the first colored coating film with a second colored coating material (Y) containing a carbon black pigment (A), and at least one (B) of a perylene black pigment (B1) and two or more pigments (B2) selected from the group consisting of blue pigments, red pigments, yellow pigments, and green pigments, to form a second colored coating film; Step (3): A step of applying a clear coating (Z) onto the second colored coating film to form a clear coating film; and Step (4): A method for forming a multilayer coating film, comprising a step of heating the first colored coating film formed in step (1), the second colored coating film formed in step (2), and the clear coating film formed in step (3) separately or simultaneously to cure them, The lightness L of the multi-layer coating film ＊ (45°) is 4 or less, and Chroma C of the multi-layer coating film ＊ (45°) is 2 or less, and A method for forming a multi-layer coating film, characterized in that at least one of the diffuse reflectance at a wavelength of 905 nm and the diffuse reflectance at a wavelength of 1550 nm of the multi-layer coating film is 10% or more.

2. The method for forming a multilayer coating film according to claim 1, wherein the value obtained by multiplying the cured film thickness (μm) of the second colored coating film by the pigment weight concentration (%) of the carbon black pigment (A) in the second colored coating material (Y) is within the range of 5 to 25.

3. 3. The method for forming a multi-layer coating film according to claim 1, wherein the pigment weight concentration of the carbon black pigment (A) in the second colored coating material (Y) is within the range of 0.2 to 5%.

4. The method for forming a multilayer coating film according to any one of claims 1 to 3, wherein the second colored coating material (Y) contains the perylene black pigment (B1), and the pigment weight concentration of the perylene black pigment (B1) is within the range of 3 to 12%.

5. The second colored coating material (Y) contains two or more pigments (B2) selected from the group consisting of blue pigments, red pigments, yellow pigments, and green pigments, and the total pigment weight concentration of the pigments (B2) is within the range of 3 to 12%. The method for forming a multilayer coating film according to any one of claims 1 to 3.

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