Low light reflectance, low-fungibility coatings

Abstract

A method for coating a substrate to form an opaque light-absorbing film, comprising: (a) preparing a suspension by suspending (i) a pigment, (ii) a binder including a polysiloxane, polyol, or a combination thereof, (iii) a rheology modifier, and (iv) an adhesion promoter containing a silane group in a solvent; (b) spray coating the suspension onto a substrate, wherein, in order to form a porous coating, most of the solvent is evaporated before the suspension comes into contact with the substrate; (c) repeating step (b) until the average film thickness is at least 20 μm; and (d) curing the coating to obtain a Δ haze value (measured on glass in accordance with ASTIM-D1003-21) of less than 1 and a fog number of at least 95 measured in an extended SAE-J1756 photometric test at 120°C, 168 hours, and a collector plate temperature of 21°C.

Description

Technical Field

[0001] The present invention relates to the manufacture and application of a black coating with a very low reflectivity, which has low fogging property (glass clouding property), is less likely to generate haze, and is used to protect an Advanced Driver Assistance System (ADAS) sensor from stray light.

Background Art

[0002] The use of imaging systems in automobiles is now common, and a significant percentage of new cars use camera systems to enhance driver safety. Camera systems are generally protected from sunlight and veiling glare by shields that employ various techniques to absorb stray light. An example of this is shown in U.S. Patent Publication No. 2021-0306537, "Vehicular windshield-mounted forward viewing camera with coated stray light shield region of housing".

[0003] An Advanced Driver Assistance System (ADAS) is a series of technologies (both hardware and electronics) designed to assist a driver during driving and parking operations. This system automates part of the driver's function and is designed to help reduce the number of traffic accident fatalities caused by driver error by using various types of sensor systems to understand the environment around the vehicle.

[0004] The main external vision sensors used in ADAS are camera systems (front, side, rear), long-range / short-range radar, ultrasonic waves, and LiDAR (lidar).

[0005] Sensors that use visible light or infrared light, such as cameras and LiDAR, need to be protected from stray light from the surrounding environment, including the sun, headlights of oncoming cars, and overhead streetlights. If the sensor is not protected, stray light can cause veiling glare and image washout, effectively "blinding" the sensor or degrading its performance, preventing the ADAS system from functioning correctly.

[0006] As automobiles become increasingly automated with sophisticated computer-controlled autonomous driving functions, malfunctions in sensor systems due to poor control of stray light can lead to accidents.

[0007] Most systems designed to protect such sensors from stray light use a combination of baffles and light-absorbing coatings, commonly known in the automotive industry as glare shields. In ADAS systems, front and side cameras are often surrounded by glare shields made of injection-molded polymer with textured surfaces, black flocking, molded baffle ridges, and simple black paint to minimize stray light reaching the cameras. For ADAS1 functions such as adaptive driving control, emergency brake assist, automatic emergency brake assist, lane keeping, and lane centering, this design functions to an acceptable level. When ADAS functionality increases to ADAS Level 2 (ISO2), where features such as automatic parking and other features that allow the vehicle to autonomously accelerate, brake, and steer are performed, sensor protection becomes even more critical. At ADAS Level 2, the driver still needs to be attentive and in the driver's seat at all times. If the ADAS control system "drops out" while the vehicle is moving at high speed, the driver can take over driving at any time or in an emergency. Dropouts typically occur under harsh lighting conditions where the sensor's signal-to-noise ratio exceeds the software's safety limits.

[0008] As you progress from ADAS2 to levels 3, 4, and 5, the level of interaction between the driver and the vehicle decreases significantly, with level 5 being fully autonomous, eliminating the need for a steering wheel or driving control systems that involve the occupants. Any malfunctions in ADAS level 2+ optical sensors, or anything that reduces their ability to accurately judge the environment surrounding a vehicle moving at high speeds, have a high potential to cause the vehicle to break down or lead to dangerous driving situations where the control system cannot detect stationary obstacles, moving vehicles, or pedestrians.

[0009] With these advancements in automation, stray light control and camera shield design have become far more important. Conventional invisible light-absorbing coatings used for stray light control no longer provide sufficient performance, as they degrade and contaminate sensors and windshields due to thermal fogging and outgassing throughout the vehicle's lifespan. Furthermore, they contain materials such as carbon nanotubes and graphene, which are potentially dangerous to occupants and unacceptable in the automotive industry. The emergence of wide-angle (FOV) glare shields and glare shields with multiple cameras has increased the surface area of ​​the shield, significantly increasing the attack by stray light, and this is also influenced by the increased surface area of ​​the coating that causes fogging.

[0010] Historically, functional, non-aesthetic black paints for automobiles have been manufactured by combining various functionalized metal oxides and amorphous carbon pigments with binders, stabilizers such as surfactants and dispersants, adhesives, and solvent carriers that can be water-based or VOC (volatile organic compound)-based. Such black paints may also contain defoamers, UV stabilizers, and biocides. In such functional, non-aesthetic matte black paints used as light absorbers for automobiles, keeping the level of fogging very low has not been a concern. This is because such properties were not required in early ADAS systems, and until recently, coating manufacturers had not tested or researched the coating elements that contribute to fogging. Even after ADAS manufacturers noticed that heavy fogging on windshields and camera lenses reduced optical performance, they thought that it could be reduced to an acceptable level simply by baking after spraying.

[0011] Note: The automotive terms "low-fogging" and "fogging" as used in this application should not be confused with anti-fogging, low-fogging, anti-misting, or low-misting surface coatings or treatments (e.g., those disclosed in US 2012 / 0295084 A1) designed to protect coated objects (e.g., mirrors) from mist or fogging in humid environments such as shower rooms. This type of superhydrophobic coating can also be colored with pigments to color the glass or surface to which it is applied. In contrast, in this application, "low-fogging" means a non-transparent black coating that does not emit condensable material (fog) that absorbs light and, when heated under dry or humid conditions, accumulates on glass or optical surfaces, blurring the view through the glass or lens.

[0012] Furthermore, it should be noted that when sunlight hits fog condensed on the windshield, diffuse flare is likely to occur on the windshield from a given sun position. This flare further limits the camera's field of view, leading to a further decrease in performance and safety.

[0013] As automation in automotive systems increases and safety requirements become increasingly stringent, using light-absorbing coatings that cause fogging and degrade sensor performance during a vehicle's lifespan is no longer acceptable. Since driving functions become more autonomous, it is crucial that they do not degrade, thus necessitating new light-absorbing solutions that overcome the limitations of existing black coatings and baffles used to trap light in ADAS camera shields and automotive head-up display (HUD) systems.

[0014] Today's typical camera shield coatings include conventional matte black paints such as Vantablack VBx2 (a product of the present applicant, disclosed in WO 2019 / 073210) and Nextel Black, as well as three-dimensional molded polymer materials such as black flocking. Nanomaterial-based super black coatings using carbon nanotubes have also been proposed, but in reality they are brittle, have high application and manufacturing costs, and are quite irritating to human and animal mucous membranes. Therefore, despite having excellent THR (total hemispherical reflectance) performance and potentially low outgassing and fogging properties, they are not used inside vehicles.

[0015] Regarding optical properties, both Vantablack VBx2 and black floc have a hemispherical reflectance of approximately 1.1% in the visible spectrum, demonstrating excellent ability to trap light from any angle. However, due to their polymer fiber structure, floc shines intensely in direct sunlight. Typical THR (hemispherical reflectance) for black paints is between 3% and 10%, but their angular performance, i.e., their ability to capture photons at any angle of arrival, is low. Optically, a lower THR is desirable because the shield is better able to trap stray light, and camera software can more easily detect the difference between the shield coating and the tar macadam pavement of the road. Furthermore, having an absorbing coating that can efficiently trap stray light at any angle of arrival is highly desirable because the position of the sun varies at different times of the day and year.

[0016] For use in automotive ADAS systems, coatings ideally possess enhanced functionality and low THR (Through-Heat Reaction). Other desirable properties include low fogging, low Δ-haze, good thermal stability, good resistance to environmental degradation, good impact and vibration stability, resistance to damage during manufacturing and assembly, and the ability to be applied to molded polymer shields by simple and repeatable means in the automotive manufacturing environment. Cost per component is also a major factor in automotive manufacturing, and solutions that result in low total application costs for the above desirable properties are commercially very valuable.

[0017] While all of the above coatings exhibit some of these desirable properties, none exhibit all of them. The most important functional properties of a coating are THR, fogging, and the resulting Δ-haze value, handling, and UV / thermal stability. From an automotive perspective, fogging and outgassing occur when materials are heated by the sun, releasing volatile and condensable substances that accumulate on the windshield and system camera optics, narrowing the camera's field of view and causing significant degradation over time. For ADAS cameras, such contamination is like driving a car through a foggy environment, causing the control system to take a long time to identify external objects, misidentify them, or miss them entirely. Fogging is further exacerbated by hydrolysis, which occurs when coatings are exposed to high levels of moisture combined with heat from the sun. Moisture and heat accelerate chemical changes in polymer binders and functional groups on the pigment surface within the coating, causing fogging to occur more quickly and adhere severely to the windshield. Almost all conventionally manufactured polymer-based paints and functionalized pigments are susceptible to thermal fogging and hydrolysis, and the typical fog number for paints is between 18 and 90, assuming no fogging detectable at 100.

[0018] In the automotive industry, standard tests such as SAE J1756, ISO 6452, and DIN 75201 are used to measure the fogging rate of materials. These standard tests can simulate the fogging behavior of coatings and parts over the lifespan of a vehicle by varying the duration and temperature. Unless otherwise specified, the fog number as used in this patent is derived from the extended SAE J1756 photometric test, in which the material is exposed to a temperature of 120°C for 168 hours with a collector plate temperature of 21°C. This extended test simulates more than 6 years of operation in a hot climate and should not be confused with the much less severe SAE J1756 standard test of 3 hours at 100°C.

[0019] Camera shield coatings are intentionally black, and when the sky is clear, they are exposed to direct sunlight for most of the day, so it is clear that the shields get hotter than typical internal components of a car exposed to the same amount of sunlight. In many cases, camera shields can exceed 100°C at their hottest point in a single day in hot climates. This means that exceptional anti-fogging and thermal stability are essential for the applied coating throughout the entire lifespan of the car, otherwise the performance of the ADAS camera will deteriorate. In tropical climates, the situation is even more serious, as the heat accompanied by high humidity causes the coating to hydrolyze rapidly. In this case as well, the thick fogging that begins to narrow the camera's field of view through the windshield leads to a decrease in camera performance. The fogging generated from the coating also accumulates directly on the camera lens, and the deterioration of the camera lens performance directly affects the ADAS control system and camera software, creating an even more serious safety risk.

[0020] The Δ-haze value is a measurement of the change in light transmittance of glass due to fogging accumulation. The Δ-haze value is measured according to ASTM-D1003-21 using an appropriate transmittance measuring device. To measure the Δ-haze value, the light transmittance of the glass is measured at the start of the test, and then a light-absorbing coating is applied to the glass in a fogging system that thermally simulates the temperature and environment of the shield during the vehicle's service life. After the test is complete, the haze value is measured again, and the Δ-haze value (%) is obtained by subtracting the initial haze value from the final haze value. In this way, it is possible to understand how the optical properties of the windshield change due to fogging during the vehicle's service life.

[0021] In the case of GlareShield and its coatings, a high Δ-haze value indicates a decrease in glass transmittance due to hazing. The desirable Δ-haze value is less than 1 over the vehicle's lifespan, and this value was measured after the extended SAE J1756 fogging test. A value greater than 1 means that an unacceptable performance degradation may occur for optical cameras. Even with prolonged baking to remove volatile substances, the paint tends to have a Δ-haze value exceeding 5, and even the best values ​​after 12 hours of baking are only slightly above 2.

[0022] It should be noted that SAE fogging tests are conducted in a closed system and do not involve the concept of controlling humidity, therefore they do not consider the behavior of coatings in high-temperature, high-humidity environments where hydrolysis may occur. This explains why some coatings, such as those disclosed in WO 2019 / 073210 (Sally Nanosystems Limited), achieve acceptable SAE J1756 fog numbers and Δ-haze values ​​after prolonged curing, but do not achieve such values ​​in a humid heat test at 85°C, 90% RH for about 7 days.

[0023] Since cars are used all over the world, from arid desert regions to hot and extremely humid tropical environments, automakers cannot afford to choose light-absorbing coatings that only work in specific locations and deteriorate elsewhere. The coating must function reliably under all environmental conditions on Earth where the car is used.

[0024] Other desirable characteristics of this type of coating are resistance to large temperature changes found in the tropics and polar regions, resistance to degradation (change in blackness, cracking, peeling) when exposed to ultraviolet light, resistance to water condensation and non-damage by frosting, no generation of particles due to vibration / impact or general coating breakdown over the vehicle's service life, and the ability to be applied by an automated spraying technique without using a primer coating to an injection-molded polymer substrate that is a common source for manufacturing glare shields. Plastic primer coatings have the same fogging problem as the light-absorbing surface layer described above.

[0025] Current state of the art WO 2017 / 033027 (Surrey NanoSystems Limited) discloses a spray-coated coating with high environmental stability at THR 0.2% and meeting many of the criteria required for a good shielding coating, but this coating requires high-temperature plasma treatment (280 °C) in a dedicated vacuum plasma reactor, is easily damaged in its optical structure and thus cannot be touched after manufacturing, has a high manufacturing cost, and is limited to fields where carbon nanotubes are prohibited in many automotive parts, such as glare shields placed inside the vehicle and directly exposed to the driver.

[0026] WO 2019 / 073210 (Surrey NanoSystems Limited) discloses a spray-coated coating with a THR on the order of 1% in the visible spectrum, which can be prepared using ordinary pigments (such as carbon black-based pigments that do not contain carbon nanotubes). To have a fogging number greater than 90, the coating needs to be baked at an extended temperature of 120 °C for 3 to 5 hours. This requires additional hardware (baking kiln) and loading / storage space, resulting in a significant increase in manufacturing cost.

[0027] Even after baking, the coating hydrolyzes in a humid environment, causing fogging. This is due to the hydrolysis of the binder and the functional groups on the surface of the carbon pigment that stabilize the freshly applied paint. The coating has a dry heat Δ haze value of 1.2% - 1.5% after baking, but hydrolysis causes it to increase to an unacceptable level over the service life of the vehicle. Also, the coating has poor handling properties and the surface is damaged by physical contact, resulting in a low yield in the automotive manufacturing line.

[0028] The coating does not undergo UV degradation, but after baking, due to the change in refractive index / oxidation of the polymer substrate and the structural relaxation of the coating, the size of the pores used to trap light changes, and the THR significantly increases to 1.2%. Although the performance of this coating is considered to be the highest in the class, it produces fogging in a humid heat state and is difficult to handle due to the physically weak nature of the coating, so it is considered not suitable for more important shielding applications.

[0029] Also, to create a porous structure, this coating needs to be passed through the spray multiple times. Depending on the shape of the part to be coated, it may require the spray gun to pass through as many as 24 times. This means that it takes much longer to spray the part compared to conventional black paint, which only requires 2 - 3 passes. Even if this is acceptable because of the excellent THR, in the automotive industry, cost and throughput are emphasized, and a long cycle time has an adverse effect on the use of the product and is uneconomical for many OEMs.

[0030] Flocking (electrostatic flocking) is a well-known method used to create invisible light-absorbing surfaces on camera shields and lens hoods for DSLR (digital single-lens reflex) cameras. The best black flocks typically have a THR of 1-1.5% in the visible spectrum. Flocking involves using an adhesive base coating, which is then coated with electrostatically charged black fibers. These partially aligned black fibers create a velvety light-absorbing surface (see Figure 5). Since the base adhesive and flock fibers are polymers, they contribute significantly to fogging. They also degrade and fade under UV light, and some fibers may fall out as not all fibers are firmly fixed to the adhesive during manufacturing. Because the coating is not conductive, static electricity builds up, causing the detached fibers to move and electrostatically adhere to the windshield, camera, and its polymer lenses. Since these fibers are glossy black polymer filaments, the flocks can shine in sunlight, potentially causing image degradation depending on the sun's position. Attempts have been made to reduce fogging behavior by baking the floc at high temperatures for extended periods, but this only slightly improves the fog number, and it has been proven that even with the most expensive adhesives and fibers, the Δ-haze value remains above 2. Furthermore, baking for 12-16 hours to achieve a Δ-haze value above 2 would significantly increase the cost per part in the mass production environment of automobiles. In high-temperature and high-humidity environments, the adhesives and fibers undergo hydrolysis, causing the Δ-haze value to exceed 5.

[0031] Conventional black paints are also used in many camera shielding systems. Typically, they are combinations of black metal oxide or carbon-based pigments and binders, produced using conventional paint preparation methods known for generations. As they are conventional solid black paints, the THR is around 3% to 12%, and after drying, the pigment is completely encapsulated by the binder, resulting in a dense, poreless coating with poor angle-of-interest performance. Because this type of coating is poreless, the reflection of the coating becomes very large when the angle of arrival (AOI) of photons decreases. Optical performance is generally poor at most sun positions, and this is often counteracted by combining the shield with molded ridges or baffles to improve shielding performance. This works for conventional ADAS 0 and 1 shields, but not for more advanced autonomous systems. Furthermore, because they contain a large amount of functionalized pigments, binders, and additives, fogging is severe in both dry and wet heat conditions throughout the vehicle's lifespan, with typical extended SAE fog numbers in the 70s. Manufacturers have attempted to remove volatile components by using an additional post-spray baking process, but this fails to prevent the hydrolysis of binders and additives that remain after baking. The baking process typically takes several hours and requires temperatures high enough to distort the shape of the injection-molded plastic parts being coated. The drawback of long-term baking of conventional black paints is the increase in THR due to thermal oxidation, which causes the binder to change from transparent to milky yellow, making it difficult for photons to reach the pigment. As the performance of ADAS cameras becomes increasingly important for the safety of drivers and pedestrians, conventional black paints are no longer a suitable solution.

[0032] Some shield manufacturers attempt to solve the problem of stray light attacks by not using black absorbent paint and instead creating complex sawtooth-like protrusions on the baffle during shield molding to deflect sunlight away from the camera. While this method can solve the problems of coating application and degradation, it cannot achieve a sufficiently low THR unless coated with the product of the present invention (see Figure 4 showing the coating in Example 6 below). The sawtooth-like protrusions work well only when the sun is aligned with the direction of the protrusions, but not when the sun's position crosses the protrusions. When the design is changed to wider-angle cameras or shields, or when multiple cameras are mounted on a single shield, this method becomes ineffective and is generally no longer used for wider-angle shields or shields with multiple cameras in more safety-conscious ADAS2+ systems. It is also true that the best THR achievable with glare shields having sawtooth-like protrusions still cannot meet the stringent safety and performance requirements set by ADAS Level 2+ control system manufacturers.

[0033] As disclosed in WO 2019 / 073210 (Sally Nanosystems Limited), spray-applied coatings with a THR of the order of 1% in the visible spectrum can be prepared with conventional pigments (such as carbon black pigments). This patent was the first to demonstrate that conventional amorphous black carbon pigments could trap light uniformly and efficiently over a wide range of arrival angles by forming a highly porous pigment binder structure, but the concept of reducing fogging was not considered. Conventional black paints have always embedded and surrounded the black pigment in a binder within a solid structure to give the coating strength and durability, but the THR and angle performance were insufficient. By making the coating highly porous, the surface area is increased, allowing photons to enter and exit the porous pores multiple times before being absorbed by the pigment. Further porosity increases surface roughness, and this roughness, combined with the porosity, allows for more efficient photon trapping than conventional paints, and at any photon arrival angle. The developed coating exhibited low THR and TIS, but was extremely susceptible to physical contact, lacked abrasion resistance, and exhibited fogging under humid heat conditions. This fogging was due to the hydrolysis of the functional groups on the carbon pigment surface and the binder system necessary to create a stable liquid coating with a sufficiently long shelf life. While baking the coating reduced this heat-induced fogging, it could not prevent fogging under humid heat conditions due to the functional properties of the pigment and the characteristics of the binder used.

[0034] CN 113201272 A (SHANXI HUABAO NEW MAT CO LTD et al.) discloses a multi-color low-gloss aqueous paint primer finish composition for passenger trains. This multi-color low-gloss aqueous paint primer finish composition comprises an aqueous acrylic polyurethane finish agent and an aqueous epoxy primer. The aqueous acrylic polyurethane finish agent employs an aqueous acrylic resin containing hydroxyl groups, a self-extinction aqueous polyurethane resin, and a hydrophilic polyisocyanate curing agent as film-forming materials. The color of the paint is complexly adjusted using pigments and aqueous organic color pastes, and the aqueous epoxy primer provides adhesion to metal substrates.

[0035] WO 96 / 16109 A1 (AMERON INC) discloses a sprayable and trowelable epoxy-polysiloxane-based coating and floor finish composition which, upon curing, exhibits excellent weather resistance to sunlight and excellent resistance to chemicals, corrosion, and impact, comprising: (a) a resin component comprising a non-aromatic epoxy resin having at least two 1,2-epoxy groups per molecule, a polysiloxane, and an organooxysilane; (b) an amine curing agent component partially or entirely substituted with aminosilane; (c) an organotin catalyst; and (d) a coagulant / pigment component.

[0036] CN 109852334 A (JIANGSU CREVO SCIENCE & TECH CO LTD) discloses a two-component organic silicon casting adhesive that is resistant to settling, comprising components A and B in a mass ratio of 12 to 14:1. Component A comprises 100 parts by weight of α,ω-dihydroxyl polydimethylsiloxane, 100 to 200 parts by weight of filler, 1 to 20 parts by weight of plasticizer, 0.5 to 5 parts by weight of water remover, 0.5 to 4 parts by weight of fluid rheology aid, and 0 to 10 parts by weight of pigment. Component B comprises 100 parts by weight of curing agent carrier, 40 to 60 parts by weight of silane crosslinking agent, 10 to 20 parts by weight of silane coupling adhesion promoter, and 0.05 to 1 part by weight of catalyst. The fluid rheology aid is a dimethyl sulfoxide solution of a modified urea rheology aid. The weight % concentration of the dimethyl sulfoxide solution is 30 to 85%. [Overview of the project] [Problems that the invention aims to solve]

[0037] There is a demand for the manufacture of coatings with low light reflectivity and minimal fogging. [Means for solving the problem]

[0038] According to the first feature of the present invention, (i) Pigments and, (ii) A binder comprising a polymer having a hydrolyzable functional group (preferably polysiloxane, polyol, or a combination thereof), (iii) Rheological modifiers and (iv) Adhesion promoter containing a silane group and (a) A step of preparing a suspension by suspending in a solvent, Step (b) is a spray coating of the suspension onto a substrate, wherein in order to create a porous coating, most of the solvent is evaporated before the suspension comes into contact with the substrate. Step (c) is repeated until the average coating thickness is at least 20 μm, In order to achieve a Δ-haze value (measured on glass in accordance with ASTM-D1003-21) of less than 1 and a fog number of at least 95 measured in an extended SAE-J1756 photometric test at 120°C for 168 hours with a collector plate temperature of 21°C, the process of curing the coating (d) and A method is provided for coating a substrate to form an opaque light-absorbing film, including the following:

[0039] The inventors of this application have developed a novel method for creating a spray-applied super black absorbent coating that is stable even during long storage periods, including the temperatures found in container transport across equatorial regions, exhibits exceptionally low fogging, a low Δ-haze value, is thermally stable, does not decompose upon UV irradiation, is easy to handle, and can be spray-applied to polymer, composite, or metal glare shields.

[0040] In preferred embodiments, the pigment is a carbon black-based pigment, or a mineral-based black such as spinel black, black titania, iron oxide, manganese oxide, or mixed metal oxides. Preferably, it has a non-spherical branched structure, and most preferably, no functional groups have been added by oxidation or chemical grafting.

[0041] The rheological modifier is preferably a polyol, and may optionally contain polar or nonpolar groups (such as acrylate polyols). A polyol may also be included as a preferred binder, and depending on the embodiment, a single polyol can serve two roles: co-binder (e.g., with a polysiloxane) and rheological modifier.

[0042] The solvent-to-binder ratio is preferably 1:0.6 to 1:1.15, most preferably about 1:0.88.

[0043] The pigment-to-binder ratio in step (a) is preferably 1:8 to 1:4, most preferably about 1:5.6.

[0044] The evaporation of the solvent in step (b) can be controlled so that the resulting coating has pores with a diameter of 100 nm to 100,000 nm.

[0045] The coating in step (c) preferably has a dry film density of 1.3 g / cm³. 3 Below, the most preferred concentration is 0.3 to 0.8 g / cm³. 3 That is the case.

[0046] A dispersant may be provided, preferably a nonionic dispersant, and most preferably a dispersant having hydroxyl functionality that allows the dispersant to form covalent bonds in the crosslinked system.

[0047] The inventors of this application have found that by adding a carbon-based pigment with a highly branched structure (175 ml / 100 g or more OAN) that is suitable for automotive plastics, preferably a methylpolysiloxane binder, a catalyst, a highly volatile solvent, and a rheology modifier, it is possible to form a stable coating system that flows without clogging in a spray gun and does not require the addition of conventional additives that can cause fogging. Furthermore, they have found that any additives that need to be used should ideally be chemically bonded or crosslinked to the dry coating film so as not to interact with humid heat conditions and cause fogging.

[0048] A preferred embodiment will be described below with reference to the drawings. [Brief explanation of the drawing]

[0049] [Figure 1] This graph shows the total hemispheric reflectance (THR) from ultraviolet to near-infrared light for the coating of Example 6 of the present invention. [Figure 2] This is a graph of the total integrated scattered light measured with respect to the incident angle using a white light illumination source for the coating of Example 6. [Figure 3]These are scanning electron microscope (SEM) images showing the optical structure and porosity of the coating of Example 6, which was sprayed and cured. [Figure 4] This graph shows the THRF as a function of wavelength for glare shields coated with (the coating of Example 6) and glare shields without the coating. [Figure 5] This is an SEM image showing a flocked surface. [Modes for carrying out the invention]

[0050] Measurement of optical performance To understand how a black absorbing coating functions optically, we measure the total hemispherical reflectance (THR). This is because it is the most complete measure of reflectance and is recognized as an international standard for measuring the performance of materials with very low reflectance. It is important not to confuse this term with the general term "reflectance," as this would be misleading. For example, raw materials have low specular reflectance but are clearly not black. Other key optical methods for measuring the performance of absorbing coatings include BRDF (bidirectional reflection distribution function) and TIS (total integral scattered light). These tests reveal how light scatters at a surface for different photon arrival angles and different detector positions. Optically, the most desirable properties for a shielding coating are a low THR (less than 1%), and low total integral scattered light and BRDF. If these properties can be achieved with a material that possesses the aforementioned fundamental functional characteristics, is low-cost, and can be applied by conventional spray coating, the coating can be made suitable for stray light protection of ADAS camera systems to the point where all vehicles can be fully autonomous.

[0051] To measure THR, an integrating sphere coated with a highly reflective surface (such as barium sulfide BaSO4) is used to collect light reflected from the sample from all angles. The amount of light reflected by the sample is compared as a percentage to the amount of light reflected by a diffuse BaSO4 control. The incident light is focused at an 8-degree angle from the vertical so that the contributions of specular and diffuse reflection from the surface can be collected. Typical black pigment absorption coatings manufactured by conventional methods have a THR of 3% to 10%, and cannot improve the performance of the optical system beyond this point. Furthermore, as mentioned above, the binder / pigment system tends to cause severe fogging and is not suitable for long-term, high-level ADAS stray light protection.

[0052] A preferred embodiment of the present invention provides an improved method for coating a substrate (e.g., an automotive glare shield against stray light) with a coating that satisfies the following requirements: a very low THR (less than 1%), a low Δ-haze value (less than 0.8%) after an extended fogging test and exposure to 85°C, 90%RH for at least 14 days, an extended high-temperature fog number greater than 98, thermal stability from -70°C to 180°C, fade resistance to ultraviolet light, application to a molded polymer substrate at economical cost by conventional means without a primer layer, and feasible in automotive manufacturing.

[0053] The preferred components of this method are described below.

[0054] Binder The preferred binder is SILRES® MSE 100 (manufactured by Wacker), a methoxy-functionalized methylpolysiloxane binder that can be cured at low temperatures using a catalyst. This binder has a low refractive index and does not oxidize within the specified temperature range of the coating, so the THR does not change over the vehicle's lifespan. Once fully crosslinked, the polysiloxane binder becomes a very stable substance and is unaffected by the humid and dry heat conditions found in automotive environments (humidity is beneficial to the curing process). While this binder seems ideal, other moisture-resistant crosslinkable binders (though less effective than polysiloxane binders), such as polyols, are also selectable, provided other processes are followed, and they can be compatible with highly volatile solvents for spraying.

[0055] The following are examples of preferred polyol binders: Polyether polyol Polyester polyol Silicon glycol Polyolefin polyol Castor oil polyol Hydrogenated castor oil polyol Acrylate polyol Phenolic polyols Polyethylene polyol Polypropylene polyol Polytetramethylene ether glycol Polyethylene glycol adipic acid Polycaprolactone polyol Polycarbonate polyol Caprolactone-modified polycarbonate diol Caprolactone-modified acrylic acid polyol Silicon glycol Polybutadiene polyol, hydrogenated polybutadiene polyol Polyether polyol

[0056] A particularly preferred polyol binder is SETALUX® 1184 SS-51 (manufactured by Ornex Co., Ltd.).

[0057] While a binder cured by UV crosslinking is also stabilized against heat and humidity through crosslinking, and thus could be considered a solution, the inventors of this application have found that when such a binder is used in a porous light-absorbing coating, the UV light used to cure the binder cannot penetrate to the entire depth of the coating, resulting in partially cured layers and severe fogging in both dry and humid conditions.

[0058] pigment To create a stable paint solution, the inventors used a highly branched amorphous carbon pigment without added functionality, namely Printex Kappa 50 (formerly known as XPB 545, a product of Orion Engineered Carbons). It was found that conventional metal oxide pigments and amorphous carbon pigments, when combined with methylpolysiloxane binders, become very low-viscosity liquids, and if the pigment lacks functionality, it will easily leach out of the solution after mixing unless a considerably high concentration of dispersant is used.

[0059] The branched pigment used in the present invention exhibits partial stability in the methylpolysiloxane binder due to its high surface area and the structure enhanced by the physical interaction of pigment particles with each other in the solution. Therefore, the inventors were able to create a solution with partial stability, but this solution was too difficult to spray due to its low viscosity, and the pigment still seemed to leach out of the solution and precipitate within a few days.

[0060] Carbon black particles aggregate to form aggregates. The structure is a criterion for evaluating the shape and branching of these aggregates, and can be measured by oil absorption analysis (the OAN value is as described above). The preferred pigment used has a high structurality, and because the particles have a branched structure, dispersion becomes easier. This high structurality also provides a viscosity-enhancing effect, which contributes to the stability of the paint. Conventional carbon black pigments tend to result in very low-viscosity paints when mixed with methylpolysiloxanes, and unless conventional stabilizers are used, the pigment will gradually leach out of the solution after mixing. Finally, because the branched structure allows for interconnection without hindering the porous nature of the film during the spray coating process, the high surface area and branched structure of the pigment result in good jet blackness (i.e., a good measurement of blackness) and film cohesiveness.

[0061] Dispersant Conventional methods to address the stability of freshly applied paints involved using surfactants and dispersants. Therefore, the inventors investigated numerous dispersants in an attempt to stabilize the solution. While this worked well at manufacturer-recommended levels, as expected, all dried paint samples exhibited unacceptably severe fogging and unacceptably high THR (Total Heat Recovery). Paint dispersants are typically used at a ratio of 40% to 100% of the pigment weight, but more is required for highly branched structures. The inventors found that adding dispersants at this level resulted in very pronounced fogging, regardless of the type tested, even when attempting to chemically crosslink the pigments.

[0062] The inventors of this application were surprised to discover that paint solutions can be stabilized with Borchi® Gen DFN (manufactured by Borchers), a hydroxyl-functionalized nonionic dispersant. When used at a low concentration of about 4% of the pigment mass, this dispersant chemically bonds to and crosslinks with the dry film. When used at higher concentrations, the coating begins to fog.

[0063] Coating structure To efficiently absorb light from all angles (0-90 degrees), a low-density surface structure is necessary to scatter light that fails to enter the coating's pores. This diffusing surface roughness, or structure, is created during the coating application process. The measurement of the absorption coating performance, which absorbs and scatters light from different AOIs (angles of arrival of photons), is called TIS, or total integrated scattered light. While a surface that is strongly absorbent when viewed directly from above shows an almost constant increase in THR when viewed at incident angles greater than 45 degrees (see Figure 2, which shows the TIS of the coating of Example 6 measured against the incident angle according to the present invention), this surface structure and porosity show only minimal change even up to an AOI of 70 degrees (the limit of the measurement system), confirming that the formed structure exhibits exceptional angular characteristics compared to conventional black paints and flocking.

[0064] Many factors affect the density and surface topology of a coating, such as the distance from the spray nozzle to the surface, the type of nozzle, ambient temperature, humidity, and substrate temperature. The inventors of this application have found that the rate at which the solvent evaporates from the coating composition (while in the air or immediately after contact with the surface) is particularly important. Those skilled in the art (spray technicians, etc.) should be able to adjust these spray factors to prepare a coating of a desirable density.

[0065] The spray coating process has several parameters that inform the technician that the correct results have been achieved. The ideal surface density of the coating (when the weight of the substrate is actually measured) is 4-10 mg / cm³. 2 It should be as follows. The amount of paint needed to achieve this density depends on the coating efficiency and the number of coats applied, but it should be approximately 0.025 to 0.05 mL / cm³. 2The process is as follows: After spraying a sufficient amount onto the part, inspect it under bright, broad-spectrum white light next to a standard sample with a known THR. The apparent blackness level should be indistinguishable from all angles and the compared roughness level. There should be no obvious pinholes or inhomogeneities. If the blackness of the object being sprayed appears low and smooth, additional paint may be applied to achieve the desired roughness, thereby making the particles clearly visible on the surface under a bright, broad-spectrum torch. An inhomogeneous surface is evident from the gray areas and rough surfaces, suggesting that the paint was applied too wet, resulting in a roughened surface on the smooth underlying layer.

[0066] Coating thickness Conventional coatings manufactured using methylpolysiloxanes typically have a coating thickness limited to approximately 20 μm. A solid thin film is formed by wet spraying to ensure reliable adhesion to the coated metal substrate. Beyond this thickness, stress delamination due to heating is possible, which is unacceptable in this invention. In the case of plastic substrates, the delamination problem is even more serious, as the surface energy of the polymer substrate is significantly lower than that of metal, resulting in lower adhesion of the sprayed film. Unless the film chemically bonds to the surface, stress delamination is more severe in polymer substrates. To reduce the THR of the coating of the present invention, it is necessary to form a porous coating with a thickness exceeding 20 μm, and this was the problem that the present invention aimed to solve.

[0067] The inventors of this application have found that adding a polyol to methylpolysiloxane and a small amount (percent) of a crosslinkable dispersant removes intrinsic stress from the film, allowing the material to be sprayed correctly and the coating solution to be stabilized over a long period of time. It should be noted that it is also possible to form a film using a polyol without methylpolysiloxane, provided that all other steps are followed. Furthermore, since methylpolysiloxanes are very sensitive to humidity during long-term storage because moisture can initiate polymerization of the binder, an alkoxysilane was added to act as a moisture scavenger. Alkoxysilanes are also known to have the additional advantage of increasing adhesion to substrates with low surface energy and completely crosslinking into the resin system, thus preventing fogging.

[0068] While the addition of polyols resolved film stress and stability issues, challenges arose regarding the curing of the sprayed film. Polyols are typically cured with isocyanate agents, and if they do not cure properly and completely, the uncured polyol fragments are reactive to moist heat, causing fogging. Since isocyanates also begin reacting as soon as they are added to the paint solution, their curing also limits the pot life of the paint. For this reason, isocyanate catalysts were not considered acceptable and were not considered for application to the polymer substrate in this study.

[0069] catalyst Titanium butoxide catalysts can be used to cure methylpolysiloxanes, acting to induce hydrolysis by substituting alkoxide functional groups. The hydrolyzed species then undergo polycondensation to form cross-linked structures. Titanium butoxide catalysts can be used to substitute alkoxide groups not only in methylpolysiloxanes but also in other species containing alkoxide groups. Titanium butoxide can also be used as a catalyst for acetoxy substitution of other acetoxy functional species.

[0070] The acrylic acid polyol used by the inventors of this invention consists of an acrylic acid or alkyl ester group and a polyol functional group. As mentioned above, when using an isocyanate crosslinking agent, the polyol functional group is usually a crosslinkable species. During development, the inventors hypothesized that the polyol functional group was involved in polycondensation with hydrolyzed methylpolysiloxane. Evidence suggested that the acrylic acid or alkyl ester group could be acetoxy-substituted using a titanium butoxy catalyst. This would generate secondary species, which would then polycondense with hydrolyzed methylpolysiloxane to completely crosslink, resulting in a thermally stable, fog-free modified binder system.

[0071] The experimental results demonstrate that this is the case when a spray-applied, low-temperature cured coating is created that benefits from all the desirable functionalities for the ADAS applications disclosed herein.

[0072] porous If a stable coating that does not produce fogging after application and curing has been created, then a suitable optical structure that is porous and traps light should also be created during the spray application process so that the THR in the visible spectrum is less than 1%.

[0073] The amount of light reflected from a surface under normal incidence is proportional to the difference in refractive index between the materials at the interface, according to Fresnel's equation. Therefore, the closer the refractive index of the materials (air and coating), the closer the reflectivity tends to be to zero. In the case of certain materials, a decrease in density leads to a decrease in refractive index, resulting in a decrease in reflectivity.

[0074] solvent To achieve a low-density structure, a highly volatile solvent can be used in the spraying process that evaporates instantly as the paint leaves the spray gun, preventing solvent buildup on the sprayed film. If the solvent used does not evaporate instantly, the coating will adhere in an overly wet state, resulting in minimal porosity and a high THR (Total Heat Rate), similar to conventional black paints. One possible method using a relatively low-volatility solvent is to heat the substrate to a temperature sufficient to rapidly evaporate the solvent from the binder / pigment mixture, and to slow down the spray pass rate to ensure that the solvent from previous passes evaporates completely. However, this significantly increases the time required to coat the parts, and the need to install heaters in the spraying environment to handle evaporating and accumulating solvents is costly and poses a fire hazard, making it clearly not ideal. The only advantages of high-boiling-point solvents are lower air and sea transport costs and a simpler spray chamber system.

[0075] Many polymers used in paint manufacturing today utilize aqueous solutions or stable VOC (volatile organic compound) solvents such as xylene and toluene, designed to evaporate slowly and in a controlled manner to form a high-density, hard coating. When preparing spray paint systems from highly volatile solvents such as acetone, conventional binders and additives often fail to produce a stable solution without adding a considerable proportion of undesirable stabilizing additives (as described above). Even if a stable solution is achieved, spraying often results in clogging of the spray gun nozzle due to the rapid evaporation of the solvent, and severe fogging occurs in humid conditions because the additives are not chemically fixed within the binder. The challenge is to find a combination of binder, pigment, and volatile solvent that can fully crosslink after spraying, is stable after manufacturing, sprays continuously, allows for instantaneous solvent evaporation, and can be porous by achieving the correct THR, while possessing all the basic functional properties required for glare shielding applications.

[0076] Rheological modifier When polymer pigment dispersions were added to highly volatile solvents such as acetone, it was noticed that they remained unstable unless a rheological modifier was used. However, conventional methods resulted in severe fogging during testing, so other possibilities were explored. Literature indicates that some conventional paint formulations use binders such as PVAc (polyvinyl acetate) as stabilizers. However, experiments have shown that PVAc degrades severely under humid heat conditions. After numerous experiments with binders that could act as rheological modifiers, it was discovered that the paint could be stabilized by using an acrylic acid polyol that can be crosslinked to a film using a titanium butoxide catalyst to cure the methylsiloxane binder. This polyol also plays two roles, namely as a co-bonding agent.

[0077] When this combination of modified binders was combined with acetone and a branched carbon pigment structure, it was possible to prepare a stable paint solution with low THR without any components that would cause fogging under thermal or humid heat conditions as seen in ADAS applications. By using acetone, the binder-pigment combination could be sprayed onto the substrate by passing the spray multiple times, using a spray technique that evaporated most of the solvent before it reached the substrate. This spraying method allowed for the creation of a highly efficient porous structure with only three spray passes, and this structure was easy to handle.

[0078] The porous structure of the coating in Example 6 (see Figure 3) was created by the spray application process, where the optimal solvent / binder / pigment combination passed through the spray gun nozzle. While the fan gas rapidly atomizes the paint into small droplets of a wide range of droplet sizes, most of the solvent evaporates due to its volatility before the paint reaches the substrate to be coated. Because the solvent evaporates rapidly, these droplets consist mainly of binder and pigment, and because the solvent content decreases rapidly, they are viscous and cannot form a dense wet film upon reaching the surface, but they are able to adhere to each other. With each spray pass, small islands of pigment and binder are formed, beginning to form a coral reef-like optical structure with a porous surface roughness suitable for trapping photons. It should be noted that the distance the spray process passes through greatly affects the optical structure formed. Spraying from too close a distance results in insufficient solvent evaporation, forming a high-density, high-THR film, while spraying from too far a distance results in excessive solvent evaporation, causing the pigment and binder combination to dry too much before reaching the surface, resulting in a dusty coating lacking cohesiveness.

[0079] By curing the coating with a titanium butoxide catalyst and using a non-functionalized branched pigment, we were able to create a highly elastic coating with exceptional properties for ADAS stray light control. This coating readily adheres to polymer injection-molded parts without the need for an additional undercoat and, importantly, can be cured without the long baking times and high temperatures typically required when using silicone binders without a catalyst. This is important because catalyst-free curing temperatures can cause serious damage to plastic injection-molded shields.

[0080] It should be noted that the curing and moisture byproducts of titanium butoxide catalyst curing are water, titanium dioxide, butanol, and methanol. To achieve the best fog number, the cured parts must be subjected to rapid, low-temperature curing (80°C in air for 30 minutes) to completely remove volatile curing byproducts. The catalyst is converted into nanoscale titanium dioxide, which is completely stable and does not affect the optical properties of the coating.

[0081] The viscosity of the paint formulation is preferably adjusted by changing the solvent ratio so that the viscosity of the freshly prepared paint is 2000 to 6000 cps (Brookfield method).

[0082] The ideal solvent ratio depends on many factors, including the binder-solvent interaction, pigment particle size, and surface area. By increasing or decreasing the solvent, the correct viscosity can be achieved to atomize and supply the paint in the correct way, allowing the solution to partially dry before reaching the substrate.

[0083] experiment Measurement of total hemispheric reflectance (THR), fogging, and delta-haze. The hemispherical reflectance is measured using a Shimadzu UV-NIR 2500 spectrometer equipped with a barium sulfide integrating sphere. The test sample is placed on the measurement port of the integrating sphere and exposed to the illumination light source. The detector collects the energy reflected by the sample coating and plots the performance from 200 nm to 1400 nm. Before starting the measurement, the instrument is calibrated against a known reflectance standard.

[0084] The fogging test was performed using a Horizon Fog testing system manufactured by Thermo Fisher Scientific.

[0085] The Δ-haze test was measured using a HazeGuard system manufactured by BYK.

[0086] Coating Examples overview Examples 1 and 2 are paints that use SILRES® MSE 100 (methoxy-functionalized methylpolysiloxane manufactured by Wacker) and SETALUX® 1184 SS-51 (OH2.0% acrylic acid polyol manufactured by Ornex) as binders, and Printex Kappa 50 (manufactured by Orion Engineered Carbons) as a pigment, with acetone as the solvent and a pigment-to-binder ratio (PTB) of 1:5.5. These paints also contain GENIOSIL® XL 10 (manufactured by Wacker) as an adhesion promoter and Borchi® Gen DFN (manufactured by Borchers) as a nonionic dispersant.

[0087] Example 3 is a paint that uses SILRES® MSE 100 (manufactured by Wacker) and SETALUX® 1184 SS-51 (manufactured by Ornex) as binders, and Printex Kappa 50 (manufactured by Orion Engineered Carbons) as a pigment, with acetone as the solvent and a pigment-to-binder ratio (PTB) of 1:6.2. This paint also contains GENIOSIL® XL 10 (manufactured by Wacker) as an adhesion promoter and Borchi® Gen DFN (manufactured by Borchers) as a nonionic dispersant.

[0088] Example 4 is a paint that uses SILRES® MSE 100 (manufactured by Wacker) as a binder and Printex Kappa 50 (manufactured by Orion Engineered Carbons) as a pigment, with acetone as the solvent and a pigment-to-binder ratio (PTB) of 1:2.1.

[0089] Examples 5 and 6 are paints that use SILRES® MSE 100 (manufactured by Wacker) and SETALUX® 1184 SS-51 (manufactured by Ornex) as binders, and Printex Kappa 50 (manufactured by Orion Engineered Carbons) as a pigment, with acetone as the solvent and a pigment-to-binder ratio (PTB) of 1:6.2. These paints also contain GENIOSIL® XL 10 (manufactured by Wacker) as an adhesion promoter and Borchi® Gen DFN (manufactured by Borchers) as a nonionic dispersant. Example 6 has a catalyst load of 2.4%, which is twice the catalyst load of 1.2% in Example 5.

[0090] Furthermore, all of Examples 1 to 6 contain titanium(IV) butoxide as a catalyst.

[0091] Example 8 is a paint prepared using iron oxide black paint instead of carbon black. This paint, like Examples 1-6, contains SILRES® MSE 100 (manufactured by Wacker) and SETALUX® 1184 SS-51 (manufactured by Ornex) as binders, GENIOSIL® XL 10 (manufactured by Wacker) as an adhesion promoter, and Borchi® Gen DFN (manufactured by Borchers) as a nonionic dispersant.

[0092] The table below summarizes the quantities of materials used in Examples 1-6 and 8.

[0093] [Table 1]

[0094] Example 7 describes a two-component ethyl acetate-based polyurethane coating using SETALUX® 1184 SS-51 (manufactured by Ornex Corporation) as a binder, Solsperse M387 (manufactured by Lubrizol Corporation) as a dispersant, and Tolonate HDB 75 MX as an isocyanate crosslinking agent. Table 2 shows the amounts of materials used in this formulation.

[0095] [Table 2]

[0096] Example 9 describes a paint using SILRES® MSE 100 (manufactured by Wacker) and Zeffle GK (manufactured by Daikin Industries) as binders, and Printex Kappa 50 (manufactured by Orion Engineered Carbons) as a pigment, with acetone as the solvent and a pigment-to-binder ratio (PTB) of 1:6.2. This paint also contains GENIOSIL® XL 10 (manufactured by Wacker) as an adhesion promoter and Borchi® Gen DFN (manufactured by Borchers) as a nonionic dispersant. Table 3 shows the amounts of materials used in this formulation.

[0097] [Table 3]

[0098] Example 10 describes a paint using Macrynal SM 6826w / 43WA (manufactured by Ornex) as a binder and FW171 (manufactured by Orion Engineered Carbons) as a pigment, with water as the solvent and a pigment-to-binder ratio (PTB) of 1:1.5. This paint also contains Borchi® Gen DFN (manufactured by Borchers) as a nonionic dispersant and Additol 6393 as an antifoaming agent. Table 4 shows the amounts of materials used in this formulation.

[0099] [Table 4]

[0100] Example 1: High pigment load, high catalyst load Batches of binder, solvent, and additives were premixed using a homogenizer to a ratio of acetone:SILRES® MSE 100:SETALUX® 1184 SS-51:GENIOSIL® XL 10:Borchi® Gen DFN of 49.5:36.9:6.8:5.2:1.6 (w / w). Pigments were added to this mixture at a load of 7.1%, and the mixture was mixed using a high-shear mixer at 7000 rpm for 10 minutes to obtain 1 liter / batch paint. Before spraying, titanium(IV) butoxide was added to the paint at a load of 2.4 wt% using a homogenizer. The resulting paint was sprayed using a pressure-feed DeVilbiss GTI Pro-lite spray gun fitted with a 0.8 mm fluid tip and TE 40 air cap. The spray settings were as follows: Under typical atmospheric conditions, the test involved a fan pressure of 1 bar, a flow rate of 76 ml / min, a flow pressure of 0.5 bar, a target distance of 15 cm, and 15 spray passes. Three bead-blasted aluminum cut-out specimens were sprayed, and the coating was then cured at room temperature for up to 16 hours, followed by curing at 90°C for up to 2 hours.

[0101] The THR values ​​of the obtained coatings were 0.80–0.87% at 550 nm and 0.79–0.86% at 700 nm. The mass of the coatings was 80–100 mg, with an average mass of 6–8 mg / cm³. 2 The average film thickness was 163–209 μm. The fog number of this coating was found to be 98 under test conditions of 120°C for 144 hours (SAE J1756). This coating was appropriate in terms of fog number, THR, and thickness. The fogging, light absorption, and film thickness characteristics of this coating were suitable for its application. However, this coating lacks homogeneity and is difficult to spray without interruption, so it is not considered suitable for automated production environments.

[0102] Example (Comparative Example) 2: Low Catalyst Load Batches of binder, solvent, and additives were premixed using a homogenizer to a ratio of acetone:SILRES® MSE 100:SETALUX® 1184 SS-51:GENIOSIL® XL 10:Borchi® Gen DFN of 49.5:36.9:6.8:5.2:1.6 (w / w). Pigments were added to this mixture at a load of 7.1%, and the mixture was mixed using a high-shear mixer at 7000 rpm for 10 minutes to obtain 1 liter / batch paint. Before spraying, titanium(IV) butoxide was added to the paint at a load of 1.7 wt% using a homogenizer. The resulting paint was sprayed using a gravity-feed DeVilbiss Pro-lite S spray gun fitted with a 1.2 mm fluid tip and TE10 air cap. Spray settings were as follows: fan pressure 1.25 bar, target distance 10-15 cm, under typical atmospheric conditions. When sprayed onto two bead-blasted aluminum cut specimens, the THR values ​​were 0.86–0.90% at 550 nm and 0.86–0.90% at 700 nm. The coating mass ranged from 99–128 mg, with an average mass of 8.2–10.7 mg / cm³. 2 The average film thickness was 238–272 μm.

[0103] The fog number of this paint was found to be 94 under test conditions of 120°C for 144 hours (SAE J1756). The paint was suitable in terms of THR and thickness. However, the fog number was found to be too low and inconsistent across tests. Therefore, this paint was ultimately unsuitable for its intended application. It is believed that the curing conditions resulted in the mixture becoming unsuitable.

[0104] Example 3: Pigment Reduction Batches of binder, additives, and solvent were premixed using a homogenizer to a ratio of acetone:SILRES® MSE 100:SETALUX® 1184 SS-51:GENIOSIL® XL 10:Borchi® Gen DFN of 50.1:37.4:6.9:5.3:0.3 (w / w). Pigments were added to this mixture at a load of 6.6%, and the mixture was mixed using a high-shear mixer at 4500 rpm for 27 minutes to obtain 20 liters / batch paint. Before spraying, titanium(IV) butoxide was added to the paint at a load of 2.4 wt% using a homogenizer. The resulting paint was sprayed using a pressure-feed DeVilbiss GTI Pro-lite spray gun fitted with a 0.8 mm fluid tip and TE40 air cap. The spray settings were as follows: Under typical atmospheric conditions, with a fan pressure of 1 bar, flow rate of 80 ml / min, flow pressure of 0.5 bar, and a target distance of 15-20 cm, three bead-blasted aluminum cut specimens were sprayed with the coating. The THR values ​​were 0.79-0.89% at 550 nm and 0.79-0.89% at 700 nm. The coating mass was 36-61 mg, with an average mass of 3.0-5.1 mg / cm³. 2 The average film thickness was 67-79 μm.

[0105] The fog number of this paint was found to be 97 under test conditions of 120°C for 144 hours (SAE J1756).

[0106] This paint was suitable in terms of fog number, THR, and thickness. It also exhibited good stability during storage, improved homogeneity, and allowed for successful spraying. For these reasons, this paint was determined to be the most preferred paint.

[0107] Example (Comparative Example) 4: Without additives Batches of binder and solvent were premixed using a homogenizer to a ratio of acetone:SILRES® MSE 100 of 5.4:3 (w / w). Pigment was added to this mixture at a load of 14.8%, and the mixture was mixed using a high-shear mixer at 7000 rpm for 6 minutes to obtain 1 liter / batch of paint. Before spraying, titanium(IV) butoxide was added to the paint at a load of 2.4 wt% using a homogenizer. The resulting paint was sprayed using a gravity-feed DeVilbiss Pro-lite S spray gun fitted with a 1.2 mm fluid tip and TE10 air cap. Spray settings were as follows: fan pressure 1.25 bar, target distance 10-15 cm, and typical atmospheric conditions. When sprayed onto three bead-blasted aluminum cut specimens, the THR values ​​were 1.1-1.3% at 550 nm and 1.1-1.4% at 700 nm. The mass of the sampled specimens ranged from 73 to 219 mg, with an average mass of 1 to 18 mg / cm³. 2 The average film thickness was 110–262 μm.

[0108] The fog number of this paint was found to be 99 under extended SAE J1756 test conditions of 120°C for 96 hours. The paint was suitable in terms of fog number and thickness. However, the THR value of the applied coating was higher than expected, and it lacked stability during storage, leading to premature separation and making it unsuitable for shipment. Furthermore, the paint's instability caused the spray gun to clog repeatedly, preventing uninterrupted spraying. For these reasons, this paint was not suitable for its intended application.

[0109] Example 5: Low catalyst load under controlled humidity curing conditions Batches of binder, solvent, and additives were homogenized to a ratio of acetone:Silres MSE 100:Setalux:Geniosil XL 10:DFN of 50.1:37.4:6.9:5.3:0.3 (w / w). Pigment was added to this mixture at a load of 6.4%, and the mixture was mixed using a high-shear mixer at 4500 rpm for 27 minutes to obtain 20 liters / batch of paint. Before spraying, titanium(IV) butoxide was added to the paint at a load of 2.4 wt% using a homogenizer. The resulting paint was sprayed using a pressure-feed DeVilbiss GTI Pro-lite spray gun fitted with a 0.8 mm fluid tip and TE10 air cap. The spray settings were as follows: fan pressure 2.5 bar, flow rate 80 ml / min, flow pressure 1.5 bar, target distance 15-20 cm, under typical atmospheric conditions. Five fog discs, prepared by buffing a substrate and baking it in an oven at 120°C for 3 hours, were sprayed together with three aluminum proof specimens that had been bead-blasted. The THR values ​​of the specimens were 0.6-0.7% at 700 nm, and their thicknesses were 163-215 μm. The sprayed substrates were then cured in an ambient environment at 35°C and 50% RH for 1 hour, followed by baking at 90°C for 30 minutes.

[0110] The fog number of this coating was found to be 99 under the extended SAE J1756 test conditions (120°C for 96 hours). This reinforced the idea that the poor fogging results in Example 2 were due to incomplete curing caused by inappropriate curing conditions, and not due to catalytic loading.

[0111] Example 6: Curing conditions under high catalyst load and humidity control Batches of binder, solvent, and additives were homogenized using a homogenizer to a ratio of acetone:Silres MSE 100:Setalux:Geniosil XL 10:DFN of 50.1:37.4:6.9:5.3:0.3 (w / w). Pigment was added to this mixture at a load of 6.4%, and the mixture was mixed using a high-shear mixer at 4500 rpm for 27 minutes to obtain 20 liters / batch of paint. Before spraying, titanium(IV) butoxide was added to the paint at a load of 2.4 wt% using a homogenizer. The resulting paint was sprayed using a pressure-feed DeVilbiss GTI Pro spray gun fitted with a 0.8 mm fluid tip and TE10 air cap. The spray settings were as follows: fan pressure 2.0 bar, flow rate 100 ml / min, flow pressure 1.5 bar, target distance 15-20 cm, under typical atmospheric conditions.

[0112] After a 168-hour fogging test at 120°C, the fog number was 99, the THR was 0.85% (see THR in Figure 1), and the Δ-haze value was less than 0.4%. No hydrolysis was observed, there was no fading due to UV exposure, and the coating exhibited good handling and environmental resistance. It also had extreme temperature resistance up to 180°C without any change in THR, and showed very good absorption from all photon arrival angles. It was sprayable using a conventional paint spray system. The THR value of the coating was 0.8-0.84 at 700 nm, and the thickness was 125-149 μm.

[0113] Example 7: Two-component polyurethane paint Batches of binder, solvent, and dispersant were premixed using a homogenizer to a ratio of SETALUX® 1184SS-51:ethyl acetate:Solsperse® M387 of 38:61:1 (w / w). The pigment was added over 4 minutes while the liquid portion was mixed at high shear at 3000 rpm. After all the pigment had been added, the paint was mixed at high shear at 7000 rpm for 4 minutes, resulting in a pigment load of 25.3%. This pigment is a low-structure, medium-to-low VOC (volatile organic compound) pigment with a primary particle size of 11 nm. It is thought that large clumps were broken up during high shear mixing, making it unlikely that this primary particle size was achieved. Before spraying, the isocyanate crosslinking agent Tolonate HDB 75 MX was added to the paint at a load of 5.3%. This paint was sprayed using a gravity-feed DeVilbiss Pro-lite S spray gun fitted with a 1.2 mm fluid tip and TE10 air cap. The spray settings were as follows: air pressure 2.75 bar, needle opened one full turn, target distance 10-15 cm, 10 spray passes, under typical atmospheric conditions. The resulting coating was dried at 30°C for 15 minutes and baked in an oven at 80°C for 30 minutes.

[0114] This coating had a THR of 0.83% at both 550nm and 700nm, and a fog number of 92%. This fog number is lower than that of the silicone-based material in the above examples, making it less desirable. Possible reasons for this low fog number include the inability to remove high-boiling point solvents during the drying stage, resulting in uncured polymer fragments remaining in the finished coating. The M387 dispersant is also considered a source of fogging.

[0115] Example 8: Paint with iron oxide pigment Batches of binder, solvent, and additives were premixed using a homogenizer to a ratio of acetone:SILRES® MSE 100:SETALUX® 1184 SS-51:GENIOSIL® XL 10:Borchi® Gen DFN of 50.1:37.4:6.9:5.3:0.3 (w / w). A 7.3% pigment was added to this mixture, and the mixture was mixed using a high-shear mixer at 6000 rpm for 3 minutes, 5500 rpm for 7 minutes, and then 6000 rpm for 5 minutes to obtain a 1 liter / batch paint. The paint began to settle immediately after mixing and was unsuitable for spray applications. When applied to a cut specimen, the mixture dried, leaving most of the substrate exposed, highlighting the paint's instability. For this reason, FeO paint was found unsuitable for this formulation.

[0116] Example 9: Fluorinated copolymers for rheology Batches of binder, solvent, and additives were homogenized to a ratio of acetone:Silres MSE 100:Zeffle GK:Geniosil XL 10:DFN of 50.1:37.4:6.9:5.3:0.3 (w / w). Pigment was added to this mixture at a load of 6.6%, and the mixture was mixed using a high-shear mixer at 4500 rpm for 27 minutes to obtain 20 liters / batch of paint. Before spraying, titanium(IV) butoxide was added to the paint at a load of 2.4 wt% using a homogenizer. The resulting paint was sprayed using a DeVilbiss GTI Pro pressure-feed sprayer fitted with a 0.8 fluid tip and TE10 air cap. The spray settings were as follows: fan pressure 2.0 bar, flow rate 100 ml / min, flow pressure 1.5 bar, target distance 15-20 cm, 10 spray passes, under typical atmospheric conditions.

[0117] The corresponding fog number for this paint was found to be 97 under extended SAE J1756 test conditions (120°C for 168 hours). The THR value was 1-1.3% at 700 nm, and the thickness was 100-150 μm.

[0118] Example 10: Aqueous acrylic acid polyol Batches of binder, solvent, defoamer, and dispersant were mixed in the ratio Macrynal SM 6826 w / 43 WA: water: Additol VXW 6393: Borchi Gen DFN of 17.8:79.2:0.1:2.9 (w / w). This mixture was high-shear mixed at 3000 rpm for 3 minutes until chemical bonding occurred. The pigment was added at a load of 10% and high-shear mixed at 3000 rpm for 6 minutes, and then at 5000 rpm for another 6 minutes. This pigment is a high-structure medium-to-low VOC (volatile organic compound) pigment with a primary particle size of 11 nm. It is thought that large clumps were broken up during high-shear mixing, making it unlikely that this primary particle size was achieved. Before spraying, the isocyanate crosslinker Easaqua M 501 was added to the paint at a load of 4.2%. This paint was diluted with water to a sprayable viscosity. Next, the coating was sprayed using a gravity-feed DeVilbiss Pro-lite S spray gun equipped with a 1.2mm fluid tip and TE10 air cap. The spray settings were as follows: air pressure 2.75 bar, needle opened 1 turn, target distance 10-15 cm, 20 spray passes, under typical atmospheric conditions. The resulting coating was baked in an oven at 100°C for 1 hour.

[0119] The THR of this coating was 1.1% at both 550nm and 700nm, the fog number was 96 under extended SAE J1756 test conditions (120°C for 168 hours), and the average film thickness was 120 μm. The fog number of this coating is lower than that of the silicone-based material in the above examples, and is therefore undesirable. The reason for this low fog number is thought to be the defoaming agent necessary to make the solution stable. The THR is higher than all the other examples, but is within the acceptable range. The reason for this high THR is most likely that water has a higher boiling point than acetone, and because of the higher boiling point, it is necessary to wait for the water to evaporate after each pass of the spray. Finally, the water-based coating had poor adhesion to the plastic substrate and required multiple passes of the spray to achieve the appropriate optical properties (20). It is thought that plasma activation of the polymer surface before spraying may improve adhesion.

[0120] Any preferred features or modifications of the embodiments and dependent claims described herein are applicable to any feature of the invention taught herein. Furthermore, each feature of the dependent claims, as well as any preferred features or modifications of the embodiments described herein, are all combinable and interchangeable with one another.

[0121] The disclosures of UK Patent Application No. 2306695.4, which form the basis of the priority claim of this application, and the disclosures of the abstract of this application are incorporated herein by reference.

Claims

1. (i) Pigments and (ii) A binder comprising a polysiloxane, a polyol, or a combination thereof, (iii) Rheological modifiers and (iv) Adhesion promoter containing a silane group and (a) A step of preparing a suspension by suspending in a solvent, Step (b) is a spray coating of the suspension onto a substrate, wherein in order to create a porous coating, most of the solvent is evaporated before the suspension comes into contact with the substrate. Step (c) is a process in which step (b) is repeated until the average film thickness is at least 20 μm, In order to set the Δhaze value (measured on glass in accordance with ASTIMM-D1003-21) to less than 1 and the fog number measured in the extended SAE-J1756 photometric test at 120°C for 168 hours with a collector plate temperature of 21°C to at least 95, the process (d) involves curing the coating. A method for forming an opaque light-absorbing film by coating a substrate with the following:

2. The method according to claim 1, wherein the pigment is a carbon black-based pigment, or a mineral-based black such as spinel black, black titania, iron oxide, manganese oxide, or mixed metal oxide.

3. The method according to claim 1 or 2, wherein the pigment has a non-spherical branched structure.

4. The method according to any of the preceding claims, wherein the oil absorption rate (OAN) of the pigment (measured by ASTM 2414-22) is 100 cc / 100 g to 630 cc / 100 g.

5. The method according to any of the preceding claims, wherein the pigment does not have functional groups added by oxidation or chemical grafting.

6. The method according to any of the preceding claims, wherein the binder is methoxysilane, ethoxysilane, phenoxysilane, or a combination thereof.

7. The method according to any of the preceding claims, wherein the rheological modifier is a polyol having a polar group and a nonpolar group as an option.

8. The method according to claim 7, wherein the rheological modifier is an acrylic acid polyol.

9. The method according to any of the preceding claims, wherein the adhesion promoter comprises an alkoxy epoxy silane or an alkoxy vinyl silane.

10. The method according to any prior claim, wherein the solvent is ethyl acetate, acetone, methyl ethyl ketone, or a combination thereof.

11. The method according to any of the preceding claims, wherein the solvent-to-binder ratio is from 1:0.6 to 1:1.

15.

12. The method according to any of the preceding claims, wherein the evaporation of the solvent in step (b) is controlled such that the resulting coating has pores with a diameter of 100 nm to 100,000 nm.

13. The method according to any of the preceding claims, wherein the shape of the pigment is particulate.

14. The method according to claim 13, wherein the average particle size of the pigment particles is 11 nm to 250 μm.

15. The method according to any of the preceding claims, wherein the ratio of pigment to binder in step (a) is 1:8 to 1:

4.

16. The method according to any of the preceding claims, wherein the boiling point of the solvent is less than 90°C.

17. The method according to any of the preceding claims, wherein the viscosity of the suspension in step (a) after stirring is 1500 to 6500 cps (Brookfield viscosity).

18. The dry film density of the coating in step (c) is 1.3 g / cm³. ３ The method according to any of the prior claims, which is as follows:

19. The dry film coating rate of the substrate obtained from step (b) is 3 mg / cm². ２ ~8 mg / cm³ ２ The method according to any of the prior claims.

20. The method according to any of the preceding claims, wherein the suspension comprises a catalyst that helps cure the coating.

21. The method according to claim 20, wherein the catalyst is titanium butoxide.

22. The method according to any of the preceding claims, wherein the suspension comprises a dispersant.

23. The method according to claim 22, wherein the dispersant is a nonionic dispersant.

24. The method according to claim 22 or 23, wherein the mass of the dispersant is 4% or less of the mass of the pigment.

25. The method according to any one of claims 22 to 24, wherein the dispersant includes hydroxyl functionality that enables the dispersant to form covalent bonds in the crosslinked system.

26. The method according to any of the preceding claims, wherein the pigment does not contain carbon nanotubes.

27. The method according to any of the preceding claims, wherein the adhesion promoter is trimethoxyvinylsilane.

28. A coated substrate obtained by the method described in any of the preceding claims.

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