Anti-reflective black coating composition and optical instrument

Abstract

To provide an antireflection black coating composition having good antireflection characteristics in an infrared region used particularly in LiDAR equipment or the like, and excellent in adhesion to a housing of the equipment mainly made of aluminum.SOLUTION: The antireflection black coating composition contains a solvent, an epoxy resin, a cationic thermal initiator, a black pigment, and a silica filler, wherein the silica filler contains an air layer therein and has a reflectivity of 2.5% or less to light having a wavelength of 1,500 nm in measurement of total light reflectivity at an incident angle of 8 ° in a cured dry coating film.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an anti-reflective black coating composition and an optical device. Specifically, the present invention relates to a black coating composition having anti-reflective properties, and particularly to a black coating composition suitable for the interior and exterior of ADAS (Advanced Driver-Assistance Systems) devices. [Background technology]

[0002] In recent years, various sensors have been widely used to realize improvements in automobile safety and advances in autonomous driving technology. Among these, various cameras and LiDAR (Light Detection and Ranging, or Laser Imaging Detection and Ranging) devices are used as devices that optically collect information such as the distance and direction of objects.

[0003] Aluminum components are often used in automotive ADAS devices, specifically front cameras and LiDAR devices, due to their heat resistance, ease of processing, and cost. To further improve corrosion resistance, the surface is often treated with cathodic electrodeposition coating or anodizing, and most of these are black. While these devices require high precision, optical noise such as flare and ghosting caused by external light must be suppressed, as it affects the operation of the aforementioned devices. In particular, LiDAR often uses infrared light, so improved optical properties in the infrared wavelength range are required.

[0004] In the field of optical equipment, coating materials such as those described in Patent Document 1 have been widely used as anti-reflection coating materials. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-101402 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the paint described in Patent Document 1 does not take into consideration the reflectance in the infrared wavelength range used in LiDAR devices, but is only concerned with the reflectance in the visible light range. Furthermore, in order to achieve low reflectance, it is necessary to simultaneously achieve adhesion to the substrate surface (aluminum member), but the prior art does not mention this point.

[0007] Therefore, an object of the present invention is to provide an anti-reflective black coating composition that has good anti-reflective properties, particularly in the infrared region used in LiDAR devices and the like, and that has excellent adhesion to the housings of the above devices, which are mainly made of aluminum. [Means for solving the problem]

[0008] The anti-reflective black coating composition of the present invention contains a solvent, an epoxy resin, a cationic thermal reaction initiator, a black pigment, and a silica filler, wherein the silica filler contains an air layer therein, and when the composition is cured and dried, the reflectance for light with a wavelength of 1500 nm is 2.5% or less in total light reflectance measurement at an incident angle of 8°. [Effects of the Invention]

[0009] The anti-reflective black coating composition of the present invention has good anti-reflective properties, particularly in the infrared region used in LiDAR devices and the like, and also has excellent adhesion to the housings of the above devices, which are mainly made of aluminum. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram for explaining the cross-cut test. [Figure 2] FIG. 2 is a diagram for explaining the cross-cut test. DETAILED DESCRIPTION OF THE INVENTION

[0011] Modes (embodiments) for carrying out the present invention will be described in detail. The present invention is not limited to the contents described in the following embodiments. Furthermore, the components described below include those that can be easily imagined by a person skilled in the art and those that are substantially the same. Furthermore, the configurations described below can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the configurations can be made within the scope of the gist of the present invention.

[0012] An antireflective black coating composition according to an embodiment contains a solvent, an epoxy resin, a cationic thermal initiator, a black pigment, and a silica filler, the silica filler containing an air layer. Furthermore, when the antireflective black coating composition is cured and dried, the reflectance for light with a wavelength of 1,500 nm is 2.5% or less in a total light reflectance measurement at an incident angle of 8°. Therefore, a cured and dried coating film prepared using the antireflective black coating composition has excellent antireflective properties, particularly in the infrared region used in LiDAR devices, and also has excellent adhesion to the housing of the device, which is primarily made of aluminum. In other words, when the antireflective black coating composition is applied to an aluminum component used in LiDAR devices, reflection on the surface of the component can be suppressed, thereby suppressing optical noise.

[0013] The black low-reflection film of Patent Document 1 contains a porous black pigment with a porosity of 50% or more and a binder component in a volume ratio of 50:50 to 100:0, and has a roughness parameter Rt of 0.15 to 5 μm, Ra of 0.01 to 0.5 μm, and L *The maximum specular reflectance is 20 or less, the maximum diffuse reflectance is 2% or less, and the maximum light transmittance is 5% or less from 400 nm to 700 nm. Furthermore, the application of this coating is listed as products where light leakage is a problem, such as optical devices such as cameras and television displays. However, Patent Document 1 was not originally intended for use in automotive ADAS, and therefore does not describe a low-reflection coating that satisfies the requirement for optical noise suppression. Specifically, for LiDAR, a specular reflectance of 1-2% or less is desired at an incident angle of 60°, but Patent Document 1 proposes a condition of 0.8% or less at an incident angle of 10°. Furthermore, while the long wavelength region (up to 1500 nm) should also be mentioned for LiDAR, Patent Document 1 is limited to wavelengths from 400 to 700 nm. Furthermore, achieving low reflectance requires achieving good adhesion to the substrate surface (aluminum member), but Patent Document 1 does not address this point.

[0014] As the solvent, a known solvent capable of dissolving epoxy resins is used. Considering that the anti-reflective black coating composition is used by spray coating, the solvent is preferably, for example, toluene, ethyl acetate, PGMAc (propylene glycol monoethyl ether acetate), etc. Furthermore, the solvent may be a single solvent or a mixture thereof.

[0015] Although any type of epoxy resin can be used, it is preferable to use a solid epoxy resin, which is a film-forming component, in combination with a liquid epoxy resin for adjusting the adhesion of the coating film. The solid epoxy resins may be used alone or in combination of two or more. Furthermore, the liquid epoxy resins may be used alone or in combination of two or more. The solid epoxy resin preferably has a softening point of, for example, above 90°C so that a coating film can be formed after the solvent has dried. Examples of such solid epoxy resins include HP-7200HHH (trade name) (dicyclopentadiene-type epoxy resin, softening point 95°C) manufactured by DIC Corporation, and JER 1004FS (trade name) (bisphenol A-type epoxy resin, softening point 100°C) and JER 4007 (trade name) (bisphenol F-type epoxy resin, softening point 108°C) manufactured by Mitsubishi Chemical Corporation. Furthermore, the liquid epoxy resin may be liquid at room temperature (25°C), for example. An example of such a liquid epoxy resin is EPICRON 850-S (trade name) (bisphenol A type epoxy resin) manufactured by DIC Corporation.

[0016] Known cationic thermal initiators can be used. The cationic thermal initiators may be used alone or in combination. The cationic thermal initiator may be an initiator used as a photopolymerization initiator. Such photopolymerization initiators can generate acid at high temperatures without exposure to light, thereby curing epoxy resins. To ensure sufficient adhesion to the coating, particularly to aluminum (e.g., aluminum alloys such as A5052), a curing procedure can be used, for example, by drying the solvent at 80°C for 10 minutes and then curing the epoxy resin at 180°C for 60 minutes. From this perspective, the initiation temperature of the cationic thermal initiator, i.e., the reaction initiation temperature measured by DSC (Differential Scanning Calorimetry) when the cationic thermal initiator and the epoxy resin are mixed, is preferably 120°C or higher and 150°C or lower. Examples of the photopolymerization initiator that can be used as the cationic thermal reaction initiator include arylsulfonium salts, aryliodonium salts, allene-ion complexes, quaternary ammonium salts, aluminum chelates, boron trifluoride amine complexes, etc. The anion moiety of the salts is, for example, PF6 - , BF4 - , B(C6F5)4 - Specifically, for example, PI-2074 (trade name) (aryl iodonium salt) manufactured by Rhodia, San-Aid SI-150L (trade name) (aryl sulfonium salt) manufactured by Sanshin Chemical Industry Co., Ltd., and the like are preferably used.

[0017] Known black pigments can be used. These black pigments may be used alone or in combination of two or more. Carbon black is preferably used as the black pigment. From the viewpoint of anti-reflection effect, the average particle diameter of the carbon black is preferably 40 nm or more and 60 nm or less. The average particle diameter is the arithmetic mean diameter determined by observing carbon black particles under an electron microscope. Examples of such carbon black include #3050B (trade name) (d=50 nm) manufactured by Mitsubishi Chemical Corporation.

[0018] Silica fillers are used for the purpose of reducing reflectivity. Silica fillers may be used alone or in combination of two or more. From the viewpoint of anti-reflection properties, silica fillers have air layers (voids) inside the filler, particularly to diffusely reflect light inside the particles. Here, "having air layers (voids) inside" does not mean that the inside is an air layer and the outer layer is made of SiO2, like a balloon. Specifically, silica fillers with air layers scattered inside spherical solid particles are preferred. In other words, silica fillers without a porous layer on the surface and containing multiple air particles are preferred. From the viewpoint of anti-reflection effect, the volume average particle diameter of the silica filler is preferably 8 μm or more and 12 μm or less. Examples of such silica fillers include HOLLOWY N-15 (trade name) manufactured by JGC Catalysts and Chemicals Co., Ltd.

[0019] The antireflective black coating composition of the embodiment may contain, as other components, dispersants, thixotropy-imparting agents, antioxidants, antifoaming agents, ultraviolet absorbers, plasticizers, and leveling agents, as long as the effects of the present invention are not impaired.

[0020] The antireflective black coating composition preferably contains an epoxy resin in an amount of 45.0 to 50.0 mass% when the total amount of the components excluding the solvent as a diluent is taken as 100 mass% on a solids basis. The cationic thermal reaction initiator is preferably contained in an amount of 0.3 to 1 mass%. The black pigment is preferably contained in an amount of 19.0 to 22.0 mass%. The silica filler is preferably contained in an amount of 27.0 to 35.7 mass%. The solvent content is preferably 60.0 to 67.0 mass parts when the components in the antireflective black coating composition are taken as 100 mass parts, as this provides a viscosity suitable for spray application and a cured, dried coating film with balanced reflective properties.

[0021] When the antireflective black coating composition of the embodiment is formed into a cured and dried coating film, the reflectance for light with a wavelength of 1500 nm is 2.5% or less in total light reflectance measurement at an incident angle of 8°. Furthermore, when the antireflective black coating composition of the embodiment is formed into a cured and dried coating film, the reflectance for light with a wavelength of 1500 nm is preferably 0.5% or less in specular reflectance measurement at an incident angle of 60°. Because the antireflective black coating composition has the above properties when formed into a cured and dried coating film, it can exhibit good antireflective properties, particularly in the infrared region used in LiDAR devices and the like. The conditions for forming a cured and dried coating film using the antireflective black coating composition when performing total light reflectance measurement and specular reflectance measurement are described in the Examples.

[0022] The method for preparing the antireflective black coating composition of the embodiment is not particularly limited. For example, a planetary stirring device is used to prepare a dispersion in which a black pigment and a silica filler are dispersed in a liquid epoxy resin. Also, a dispersion in which a solid epoxy resin and a cationic thermal reaction initiator are dispersed in a solvent is prepared. The two dispersions are then mixed to prepare the antireflective black coating composition.

[0023] In an optical device according to an embodiment, a cured and dried coating film of the anti-reflective black coating composition described above is formed on at least the exterior or interior of the housing. The optical device according to an embodiment is preferably mounted on a vehicle. The cured and dried coating film exhibits excellent anti-reflective properties, particularly in the infrared region used in LiDAR devices, and also exhibits excellent adhesion to the housing of the device, which is primarily made of aluminum. From the viewpoints of anti-reflective properties and adhesion, the thickness of the cured and dried coating film is preferably 20 μm or more and 100 μm or less.

[0024] The method for forming the cured and dried coating film is not particularly limited, and the cured and dried coating film can be formed, for example, by a coating step, a solvent drying step, and a heat curing step. Specifically, in the coating step, the antireflective black coating composition is applied to a member such as aluminum (e.g., an aluminum alloy such as A5052) by spray coating or the like. Then, in the solvent drying step, the solvent in the applied antireflective black coating composition is dried and removed. The solvent drying step can be performed, for example, at a temperature of 80°C to 100°C for 10 to 30 minutes. A heat curing step is then performed to obtain a cured and dried coating film of uniform thickness. The heat curing step can be performed, for example, at a temperature of 150°C to 200°C for 30 to 90 minutes. After the solvent drying step, the reaction of the epoxy resin is close to an uncured state. Considering the final formation of a coating film of uniform thickness, it is desirable that the epoxy resin be in a solid state, i.e., immobile, at the temperature in the solvent drying step. For this reason, as described above, the solid epoxy resin preferably has a softening point exceeding 90° C. Furthermore, since there is a concern that the adhesiveness may be reduced due to solvent residue, it is desirable that the solvent drying temperature be lower than the curing temperature of the epoxy resin (specifically, within the temperature range described above). [Example]

[0025] The present invention will be specifically described below with reference to examples. [Examples 1 to 3] A planetary mixer was used to prepare a dispersion of black pigment (carbon black, d = 50 nm) and silica filler (spherical solid particles with air spaces scattered throughout) in liquid epoxy resin (bisphenol A epoxy resin). A solid epoxy resin (dicyclopentadiene epoxy resin) and a cationic thermal initiator (aryliodonium salt, the anion of which is B(C6F5)4) were also prepared in a solvent (propylene glycol monoethyl ether acetate). - ) was dispersed in a dispersion liquid. The above two dispersion liquids were then mixed to prepare an anti-reflective black coating composition. The anti-reflective black coating composition was prepared so that each component was contained in the amount shown in Table 1.

[0026] [Comparative Example 1] A planetary mixer was used to prepare a dispersion of black pigment (carbon black, d = 50 nm) in liquid epoxy resin (bisphenol A epoxy resin). A solid epoxy resin (dicyclopentadiene epoxy resin) and a cationic thermal initiator (aryliodonium salt, the anion part of the salt is PF6) were also prepared in a solvent (propylene glycol monoethyl ether acetate). - ) was dispersed in a dispersion liquid. Next, the above two dispersion liquids were mixed to prepare a black coating composition. The black paint composition was prepared so that each component was contained in the amount shown in Table 1.

[0027] [Comparative Examples 2 to 4] A black coating composition was prepared in the same manner as in Comparative Example 1, except that the black coating composition was prepared so that each component was contained in the amount shown in Table 1.

[0028] Comparative Example 5 A black coating composition was prepared in the same manner as in Example 1, except that a black pigment (carbon black, d = 80 nm) was used instead of the black pigment (carbon black, d = 50 nm), and the black coating composition was prepared so that each component was contained in the amount shown in Table 1.

[0029] Comparative Example 6 A black coating composition was prepared in the same manner as in Example 1, except that a black pigment (carbon black, d = 28 nm) was used instead of the black pigment (carbon black, d = 50 nm), and the black coating composition was prepared so that each component was contained in the amount shown in Table 1.

[0030] Comparative Example 7 A black coating composition was prepared in the same manner as in Example 1, except that a black pigment (carbon black, d = 26 nm) was used instead of the black pigment (carbon black, d = 50 nm), and the black coating composition was prepared so that each component was contained in the amount shown in Table 1.

[0031] [Comparative Example 8] A black paint composition was prepared in the same manner as in Example 1, except that the black paint composition was prepared so that each component was contained in the amount shown in Table 1.

[0032] Comparative Example 9 A black paint composition was prepared in the same manner as in Example 1, except that silica filler (spherical solid particles with air spaces scattered within) was used instead of silica filler (spherical solid particles with air spaces scattered within), and the black paint composition was prepared so that each component was contained in the amount shown in Table 1.

[0033] [Comparative Example 10] A black paint composition was prepared in the same manner as in Example 1, except that the black paint composition was prepared so that each component was contained in the amount shown in Table 1.

[0034] [Measurement method] <Total light reflectance> Cured and dried coating films were prepared using the antireflective black coating compositions of Examples 1 to 3. Specifically, in the coating step, the antireflective black coating composition was applied to an aluminum alloy plate by spray coating. Then, in the solvent drying step, the solvent in the applied antireflective black coating composition was dried and removed. The solvent drying step was carried out under conditions of 80°C and 10 minutes. Next, a heat curing step was carried out to obtain a cured and dried coating film with a thickness of 20 μm. The heat curing step was carried out under conditions of 180°C and 60 minutes. Furthermore, the black coating compositions of Comparative Examples 1 to 10 were used to prepare cured and dried coating films in the same manner as above. The total light reflectance of the obtained cured and dried coating film was measured. Measurements were performed using a Hitachi High-Tech UH-4150 at an incident angle of 8 degrees, with wavelengths from 300 nm to 2000 nm measured in 1 nm increments. In this way, the reflectance for light with a wavelength of 1500 nm was determined in the total light reflectance measurement at an incident angle of 8 degrees.

[0035] <Specular reflectance> In the same manner as in the measurement of total light reflectance, cured and dried coating films were prepared using the antireflective black coating compositions of Examples 1 to 3. Furthermore, in the same manner as in the measurement of total light reflectance, cured and dried coating films were prepared using the black coating compositions of Comparative Examples 1 to 10. The specular reflectance of the obtained cured and dried coating film was measured. Measurements were performed using a V-770 manufactured by JASCO Corporation at an incident angle of 60 degrees and wavelengths of 200 nm to 1500 nm in 1 nm increments. In this way, the reflectance for light with a wavelength of 1500 nm was determined in the specular reflectance measurement at an incident angle of 60 degrees.

[0036] [Cross-cut test] In order to evaluate the adhesion to the aluminum alloy member, a cross-cut test was carried out in accordance with ISO 9211-4. Figures 1 and 2 are diagrams for explaining the cross-cut test. First, a cured and dried coating film 14 was prepared on an aluminum alloy plate 12 using the antireflective black coating composition of Example 1 in the same manner as in the measurement of total light reflectance. 100 grids 16 were prepared in the cured and dried coating film 14 using a cutting guide tool and a cutter (FIG. 1). Next, tape 18 (Nichiban No. 405 (trade name), manufactured by Nichiban Co., Ltd., width: 24 mm, adhesive strength: 4.73 N / 10 mm) was applied to the cured and dried coating film 14 and peeled off perpendicularly (FIG. 2). The appearance after the tape was peeled off was confirmed. The evaluation was conducted based on whether there was no peeling or whether there was partial peeling or not (⊚).

[0037] Table 1 below shows the results of the cross-cut test as well as the measurement results of the total light reflectance and regular reflectance.

[0038] [Table 1]

[0039] In Comparative Example 4, the results of the cross-cut test were poor, so measurements of total light reflectance and regular reflectance were not performed. If total light reflectance had been measured, it is believed that the reflectance would have exceeded 2.5%. In Comparative Examples 5 to 7, the total light reflectance was high to begin with, so regular reflectance was not measured. [Explanation of symbols]

[0040] 12: Aluminum alloy plate 14: Cured dry coating film 16: Grid 18: Tape

Claims

1. Solvent and Epoxy resin, a cationic thermal initiator; A black pigment; Contains silica filler, The silica filler contains an air layer therein, When the coating is cured and dried, the reflectance for light with a wavelength of 1500 nm is 2.5% or less when measured for total light reflectance at an incident angle of 8°. Antireflective black paint composition.

2. When the cured and dried coating film is formed, the reflectance to light having a wavelength of 1500 nm is 0.5% or less when measured for specular reflectance at an incident angle of 60°C. The anti-reflective black coating composition of claim 1.

3. The black pigment is carbon black, and its average particle size is 40 nm or more and 60 nm or less. The anti-reflective black coating composition of claim 1.

4. The epoxy resin includes a solid epoxy resin and a liquid epoxy resin. The anti-reflective black coating composition of claim 1.

5. A cured and dried coating film of the anti-reflective black coating composition according to any one of claims 1 to 4 is formed at least on the exterior or interior of a housing. optical equipment.

6. For vehicle installation, 6. The optical instrument according to claim 5.

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