Water-based acrylic latex paint transparent in the NIR and SWIR bands

Abstract

Water-based acrylic latex paints have a pigment-to-pigment (DOP) ratio of 0.5 to 1.5 to form coatings in which the pigment is low in concentration and highly dispersed throughout, absorbs in the visible spectrum to produce color (e.g., black), and is transparent in the NIR and SWIR bands. Variables that determine the visible absorption and NIR and SWIR transmittance include the DOP ratio, the pigment weight percentage in the paint of 1 to 2%, and the coating thickness of 2 to 4 mils. To control viscosity, the dispersant is preferably an acrylate-based block copolymer with a molecular weight greater than 2,000 grams per mole, which contains an amine-functional block for anchoring onto the pigment.

Description

[Technical Field]

[0001] Priority claims This patent application claims the benefit of priority to U.S. Application No. 17 / 932,094 (filed September 14, 2022), which is incorporated herein by reference in its entirety.

[0002] The present disclosure relates to coatings that absorb in the visible band and transmit in the near infrared (NIR) and short wavelength infrared (SWIR) bands. [Background technology]

[0003] Spectral coatings provide specified transmittance, reflectance, or absorption in different bands of the electromagnetic spectrum. Certain classes of coatings provide high absorption in the visible band and high transmission in the NIR and SWIR bands. The visible band spans approximately 400-700 nm. As used herein, the NIR band spans 800-1300 nm, and the SWIR band spans 1300-2200 nm. Coatings can be formed from plastics or paints containing SWIR-transmitting pigments or dyes, or structural layers (e.g., nanofeatures and interference layers or multilayer films). Coatings may be used to aesthetically cover or conceal some type of IR entity or device (e.g., IR-transmitting sensors (e.g., lidar on an automobile or IR communication on a mobile device), solar cells on a building, or reflective surfaces as part of a building's cool coating). Coatings provide a color (typically black) that conceals what is underneath.

[0004] U.S. Patent Application Publication No. 2021 / 0096288 (titled "Infrared Transmissive Product"; published April 1, 2021) discloses a black layer comprising a coating film layer formed by combining a transparent plastic with at least two types of dyes / pigments, which are infrared transparent and exhibit a black color when mixed together. The black layer has a thickness ranging from 5 microns to 50 microns (0.2 to 2 mils). The black layer contains a total of 50 to 150 parts by weight of dyes / pigments per 100 parts by weight of the transparent plastic.

[0005] U.S. Patent No. 7,727,418 (entitled "Infrared Transmissive Thermoplastic Composition and Articles Formed Therefrom," issued June 1, 2010) discloses a thermoplastic composition comprising a thermoplastic polymer and a combination of dyes including a black dye and a fluorescent dye, wherein the molded article is 2.0 millimeters thick and comprises the thermoplastic polymer, the black dye, and the fluorescent dye, and has a percent infrared light transmittance of 50% or more (measured at wavelengths of 800 to 1,100 nm) according to ASTM D1003-00 and a percent visible light transmittance of 15% or less (measured at wavelengths of 400 to 650 nm) according to ASTM D1003-00.

[0006] Roof coatings are used, in part, to reflect electromagnetic energy and keep buildings cool. However, white roof coatings, which are desired to reflect in the visible and NIR / SWIR bands and provide the greatest cooling effect, are often unacceptable to homeowners with visible roofs for aesthetic reasons. Black coatings, while more aesthetically acceptable, must absorb virtually all of the visible spectrum to achieve a black appearance. In addition, standard black coatings absorb in the NIR and SWIR bands, significantly increasing the temperature of the roof surface. One approach is to provide a black spectrum coating that is reflective in the NIR and SWIR bands. Another approach is to provide a white coating or aluminum alloy that is reflective in the NIR and SWIR bands, over which a black spectrum coating that is transparent in the NIR and SWIR bands is placed. Incident IR radiation passes through the coating and is not absorbed by the white coating / aluminum alloy, but is reflected back from the coating.

[0007] Tore Kolas et al., “Cool coatings with high near-infrared transmittance for coil-coated aluminum,” Solar Energy Materials and Solar Cell 196 (2019) 94-104. As described in Section 2.3, each formulation contained four key components of the coating: pigment (NIR transparent), organic polymer (high-durability commercial polyester), organic solvent, and additives (antifoam and dispersing additives). The catalyst and crosslinking additives were already included in the commercially produced polymer. In one formulation, the pigment was 5 weight percent BASF Paliogen Black S0084. The formulations were applied to pretreated aluminum sheets with an average dry film thickness (DFT) of approximately 20 μm (0.8 mil) and cured in an oven with heated air at 232°C to crosslink the polymer bonds.

[0008] Jie Qin et al., "The Optical Properties of Black Coatings and Their Estimated Cooling Effect and Cooling Energy Savings," Journal of Power and Energy Engineering, 2014, 2, 68-75, discloses a formulation for a black cool coating, which contains a pure acrylic emulsion, a black pigment, an extender pigment (e.g., talcum) that is transparent and non-reflective across the visible and NIR / SWIR bands, and other appropriate paint additives (e.g., wetting agents, dispersants, defoamers, leveling agents, and coalescing agents). To prepare the black cool coating, the acrylic emulsion and talcum were first added to a mixing setup, followed by the wetting agents, dispersants, and leveling agents. The mixture was stirred, and then a pre-made black pigment dispersion was poured into the paint mixing setup and stirred. Water was added to adjust the viscosity of the coating. The black cool coating was applied to a bare aluminum alloy substrate at a thickness of 100–150 microns (4–6 mils). As shown in Table 1, the black pigment, talcum, and dispersant were 5.0, 25.0, and 0.5 wt.%, respectively. Based on the black pigment alone, the dispersant / pigment (DOP) ratio was 0.1. This ratio provides a relatively high concentration of pigment in the coating.

[0009] Based on the application of the cool coating, the determining parameter is not the transmittance of the coating in the NIR / SWIR bands, but the total reflectance from the black cool coating and the aluminum alloy / reflective base coat. This coating can achieve total reflectance by combining the direct reflectance from the black cool coating, the transmittance of the coating, and the reflectance from the alloy or base coat. This can have the beneficial effect of reducing the transmittance specification of the coating in the NIR and SWIR bands.

[0010] U.S. Patent Application Publication No. 2021 / 0096288 mentions in paragraph

[0005] the formation of a black layer by applying a paint made from a single black pigment (e.g., carbon black or Ketjen black). However, in a section of the visible wavelength range slightly below the border with the infrared wavelength range, light transmittance increases. This suggests that a paint containing a single black pigment does not provide sufficient absorption in the visible range for a NIR / SWIR transparent coating. Summary of the Invention

[0011] Disclosed herein is a water-based acrylic latex paint having a dispersant to pigment (DOP) ratio of 0.5 to 1.5 to form a coating in which the pigment has a low concentration and is highly dispersed throughout, absorbs in the visible range to produce a color (e.g., black), and is transparent in the NIR and SWIR ranges.

[0012] In one embodiment, the variables that determine the absorption in the visible band and the transmittance in the NIR and SWIR bands include a DOP ratio of 0.5 to 1.5, a weight percentage of pigment in the paint formulation of 1 to 2 wt%, and a coating thickness of 2 to 4 mils. More typically, the DOP ratio is 0.8 to 1.5.

[0013] In an embodiment in which the visible band spans 300-700 nm, the NIR band spans 800-1300 nm, and the SWIR band spans 1300-2200 nm, the coating has an average transmittance of less than 20% in the visible band, an average transmittance of greater than 60% in the NIR band, and an average transmittance of greater than 80% in the SWIR band. Preferably, the transmittance specifications are met at each wavelength within the band. An exemplary formulation meeting these specifications includes RHOPLEX® AC-261F binder, Paliogen® Black L0086 pigment, and EFKA® PX4310 dispersant, with a DOP ratio of approximately 1; the coating dries to a thickness of 2.5 mils and has a black color.

[0014] In one embodiment, the pigment is selected to provide a cutoff wavelength between the visible and NIR bands. A single pigment may be used to provide a "black" color with the requisite spectral characteristics. Additional pigments may be included to provide colors other than black, but this may result in reduced transmission in the NIR and SWIR bands.

[0015] In one embodiment, the dispersant is a high molecular weight compound, greater than 2,000 grams per mole, to control the viscosity of the premix. The dispersant preferably comprises an acrylic block copolymer containing an amine-functional block for anchoring to the pigment.

[0016] In one embodiment, the rheology modifier is selected to provide the paint with “associative thickening.” The rheology modifier preferably comprises a hydrophobically modified alkali-soluble rheology modifier.

[0017] In one embodiment, the pigment is mixed with a dispersant to provide a DOP ratio of 0.5 to 1.5. Mechanical crushing energy is applied to the premix to deagglomerate the pigment particles. The premix is ​​then mixed with a solvent, a binder, and a rheology modifier to form the coating.

[0018] In various embodiments, the paint can be used to provide a coating to aesthetically cover or conceal any type of IR body or device. For example, the paint can be applied to a substrate with transparency spanning the NIR and SWIR bands to cover the transmit and receive units of an IR sensor. Other uses for paint formulations with good absorption in the visible band and high transmittance in the NIR and SWIR bands are also contemplated by the present disclosure. [Brief explanation of the drawings]

[0019] These and other features and advantages of the present disclosure will become apparent to those skilled in the art from the following detailed description of the preferred embodiments taken in conjunction with the accompanying drawings, the contents of which are set forth below.

[0020] [Figure 1] 1 is a drawing of a water-based acrylic latex paint that absorbs in the visible band and is transparent in the NIR and SWIR bands. [Figure 2] 1 is a plot of transmission versus wavelength illustrating an embodiment of required maximum transmission in the visible band and minimum transmission in the NIR and SWIR bands. [Figure 3] 1 is a table of design space variables of pigment weight %, DOP ratio, and coating thickness to achieve specified transmittance in the visible and NIR / SWIR bands. [Figure 4] 1 illustrates an embodiment of a method for premixing a NIR / SWIR transparent pigment with a dispersant to obtain a low concentration of highly dispersed pigment. [Figure 5] Illustrates an embodiment in which a premix of pigment and dispersant is combined with a water-based acrylic latex binder and a rheology modifier to form a paint that cures at ambient temperature and pressure to form a coating. [Figure 6] 1 is a table of exemplary water-based acrylic latex paint formulations. [Figure 7] 1 is a plot of transmittance versus wavelength for exemplary paint formulations with different coating thicknesses. [Figure 8] This is an embodiment of a cover for an IR transceiver unit that transmits in the NIR and SWIR bands and produces black color. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present disclosure provides water-based acrylic latex paints that dry upon application to form coatings that absorb in the visible band to produce a visible color (e.g., black) and are transparent in the NIR and SWIR bands.

[0022] Commercially available acrylic paints are fast-drying paints made from pigments suspended in acrylic polymer emulsions and plasticizers, silicone oils, defoamers, stabilizers, or metal soaps. Most acrylic paints are water-based, but become water-resistant when dry. Water-based acrylic paints are used as latex house paints (latex is the technical term for a suspension of polymer particles in water). Inorganic or organic pigments are coloring materials that are completely insoluble or barely soluble in water. Pigment color arises because the pigment absorbs only certain wavelengths of visible light. The binding properties of this material determine the wavelength and efficiency of light absorption. Absorption across the entire visible spectrum produces black. These commercial paints also absorb light in the NIR and SWIR bands. Dispersants, typically surfactants, are substances added to suspend pigment particles in the solvent (water) to improve particle separation and prevent particle settling or agglomeration. A DOP ratio of approximately 0.2 is typical for acrylic paints. High pigment concentrations (e.g., at least 20% by weight) are required to achieve maximum coverage and visible light absorption. Rheology modifiers are typically added to the mixture to form a non-Newtonian fluid that provides "associative thickening," so that the paint does not "bead" when applied to form a coating, but remains as a uniform, thin coating. Antifoam agents are chemical additives that reduce surface tension, preventing the formation of bubbles.

[0023] Providing a waterborne acrylic latex paint that is highly absorbent in the visible range and highly transparent in the NIR and SWIR ranges without sacrificing formability properties (non-running, non-sagging, clean film, no brush marks, etc.) and ambient drying characteristics requires more than simply replacing standard colored pigments with NIR / SWIR transparent pigments.

[0024] Referring now to Figures 1 and 2, coating 10 is formed by applying a water-based acrylic latex paint that dries at ambient temperature (approximately 10-35°C) and ambient pressure (approximately 29-31 inches of mercury). Coating 10 is designed to absorb light rays 12 in the visible band 14 to produce a color (e.g., black) and transmit light rays 16 and 18 in the NIR and SWIR bands 20 and 22, respectively. In one embodiment, average transmittance 26 for the visible band 14 is less than 20%, and average transmittances 20 and 22 for the NIR band 28 and SWIR band 30 are at least 60% and 80%, respectively. Preferably, transmittance specifications are met at each wavelength within the band. Adding additional pigments to produce colors other than black may lower the transmittance specifications in the NIR and SWIR bands. For example, transmittance in the NIR may be at least 50%, and transmittance in the SWIR may be at least 70% on average.

[0025] A waterborne acrylic latex paint formulation that produces a coating 10 that meets these transmittance specifications requires pigments that have low concentrations in the dried coating (e.g., <5.2 wt%) and are highly dispersed throughout the coating (e.g., pigment particle size <0.8 microns). If the concentration is too high, transmittance in the NIR and SWIR bands will not meet specifications. If the pigment is not well dispersed, absorption in the visible band will be poor and will not meet specifications.

[0026] To achieve this, the waterborne acrylic latex paint formulation includes an acrylic latex binder, a water solvent, a pigment, a dispersant, a rheology modifier, and an antifoaming agent. The binder and dispersant components are transparent (e.g., on average greater than 90%) in the NIR and SWIR bands. The pigment has a cutoff wavelength that lies between the visible and NIR bands. Below the cutoff, the pigment is absorbing, and above the cutoff, the pigment is transparent.

[0027] The dispersant-to-pigment (DOP) ratio of this mixture is 0.5 to 1.5, more typically 0.8 to 1.5. This ensures a low concentration of pigment in the coating. To ensure high pigment dispersion throughout the coating, the dispersant preferably has a molecular weight greater than 2,000 grams per mole. Furthermore, dispersants with block copolymers containing amine-functional blocks for anchoring the pigment have superior absorption characteristics in the visible spectrum compared to lignosulfonate-based dispersants.

[0028] The rheology modifier is suitably selected to provide a non-Newtonian fluid that provides "associative thickening" to the formulation. Hydrophobically modified alkali-soluble rheology modifiers, for example, are a good choice for sag resistance because they provide associative thickening through the interconnection of hydrophobic acrylate units to form a network.

[0029] Referring now to FIG. 3 , the paint formulation variables that determine the resulting film's absorption in the visible band and transmittance in the NIR and SWIR bands are shown in Design Space Table 40, including a pigment weight percentage 42 of 1-2 wt % in the paint formulation (approximately 2.6-5.2 wt % in the dried coating), a DOP ratio 44 of 0.5-1.5, and a coating thickness 46 of 2-4 mils. More typically, the DOP ratio is 0.8-1.5. These three variables and their respective ranges define the paint formulation's design space for meeting various specifications for transmittance in the visible and NIR / SWIR bands. Compared to commercial latex paints (typically DOP ratios of 0.2) and black cool coating latex paints (DOP ratios less than 0.1), our formulations have DOP ratios of at least 0.5, more typically at least 0.8, which is critical for achieving both visible absorption and NIR / SWIR transmittance. Furthermore, the weight percentage of pigment of 1-2% is significantly less than the 5% pigment (not including talcum extender) in cool coatings and much less than the 20% pigment in commercial latex paints. Also, the coating thickness of 2-4 mils is thinner than the 4-6 mil thickness of black cool coatings. The tighter requirements for our formulations to meet transmittance specifications in both the visible and NIR / SWIR bands necessitate a different, more precise design space.

[0030] 4 and 5, dry pigment powder 50 is mixed with dispersant 52 to form premix 54. A mechanical grinding force 56 is applied to premix 58, such as by a ball milling process, to deagglomerate pigment particles 54. As previously mentioned, a preferred dispersant comprises a block copolymer that includes amine-functional blocks or "tentacles" 60 for anchoring to pigment particles 58. The tentacles form non-polar bonds with the pigment and polar bonds with water molecules. The tentacles have an affinity for water, thereby functioning to suspend the pigment particles despite the particles themselves being insoluble.

[0031] As shown in FIG. 5, the premix 54 is then mixed with an acrylic latex binder 62, a rheology modifier 64, an antifoaming agent 66, and a solvent (water) 68 to form a water-based acrylic latex paint 70. The paint 70 is applied and dried at ambient temperature and pressure to form a coating 72 in which the pigment particles 58 are suspended within the fused latex binder particles 62. With the appropriate combination of DOP ratio, pigment weight percent, coating thickness, and dispersant, the pigment particles 58 will exhibit the desired low concentration and be highly dispersed throughout the coating 72, as shown in the center diagram. If the variables and dispersants are not properly selected, the pigment particles 58 may be too concentrated, resulting in poor dispersion (top diagram), resulting in poor transmission in the NIR / SWIR bands, or the pigment particles 58 may clump together in the coating (bottom diagram), resulting in poor absorption in the visible bands.

[0032] Each component in the formulation was identified based on maximizing transparency in the NIR and SWIR bands while minimizing transparency in the visible band. However, it was observed that, depending on other factors that must be controlled during blending, dramatically different films were produced in terms of film formation and final properties. Achieving the desired final properties in the formed film is based on 1) the spectral properties of each component in the formulation (i.e., "component level"), 2) their distribution in the cast layer (i.e., "interaction level"), and 3) the structure that all the components aggregate to form within the coating (i.e., "system level").

[0033] 6 and 7, an exemplary formulation for a waterborne acrylic latex paint 80 having a black color is shown in Table 82, and transmittances 84, 86, and 88 at coating thicknesses of 2.5, 7, and 9 mils are plotted in plot 90. The transmittance of the coating (which has some absorption at the high end of the SWIR band) deposited on a glass slide was measured. The pigment was Paliogen® Black L 0096 (780 nm cutoff wavelength) manufactured by BASF SE. The acrylic latex binder was RHOPLEX® AC-261LF (an all-acrylic emulsion polymer for latex floor coatings) manufactured by Dow Inc. Testing showed that this binder exhibited greater than 90% transmittance in the visible and NIR / SWIR bands. The solvent was water. The dispersant was EKFA® PX 4310 (a copolymer containing an amine-functional block) manufactured by BASF SE. The defoamer was BYK-024 manufactured by BYK USA Inc. The rheology modifier is ACRYSOL™ DR-110 (a hydrophobically modified alkali-soluble rheology modifier) ​​manufactured by DOW Inc. The acrylic latex binder accounts for the majority of the paint's weight percentage, approximately 68.6%, with approximately half of this being water itself. The rheology modifier is 0.56 wt% and the defoamer is just 0.05 wt%. The pigment and dispersant are equal amounts at 1.4 wt%, resulting in a DOP ratio of 1. This helps maintain a low pigment concentration with very high dispersibility, which in turn helps prevent aggregation and / or uneven pigment distribution, which can reduce absorption in the visible range. In other words, maximum absorption in the visible range and high transmittance in the SWIR range are achieved with a relatively low amount of pigment. The remainder is made up of water.

[0034] As shown in plot 90, the transmission 84 for the 2.5 mil coating averages less than 20% in the visible band, more than 60% in the NIR band, and more than 80% in the SWIR band. The transmission meets specifications at nearly all wavelengths in each band. Note that the sharp drop in transmission at approximately 2300 nm is due to the acrylic latex binder. Note that the transmissions 86 and 88 for the 7 and 9 mil coatings are highly absorbing in the visible band due to the added thickness. However, the transmission does not meet specifications in the NIR / SWIR bands.

[0035] In various embodiments, the paint can be used to provide a coating to aesthetically cover or conceal any type of IR body or device. For example, the paint can be applied to a substrate with transparency spanning the NIR and SWIR bands to cover the transmit and receive units of an IR sensor. Other uses for paint formulations with good absorption in the visible band and high transmittance in the NIR and SWIR bands are also contemplated by the present disclosure.

[0036] Referring now to FIG. 8, an infrared-transmitting product 100 includes a body 102 configured to cover a transmitting unit 104 and a receiving unit 106 for NIR and SWIR light in an IR sensor 108. The body 102 includes a substrate 110 having transparency spanning the NIR and SWIR bands and a 2-4 mil thick coating 112 on the rear or front surface of the substrate. The coating layer 112 includes a water-based acrylic latex paint containing a 1-2 wt% mixture of deaggregated pigment and dispersant that is transparent in the NIR and SWIR bands. When dried, the pigment constitutes approximately 2.6-5.2 wt% of the coating. The mixture has a dispersant-to-pigment (DOP) weight ratio of 0.5-1.5 and a rheology modifier. The paint cures at ambient temperature and pressure to form a coating in which the pigment is low in concentration and highly dispersed throughout, absorbs and produces color in the visible band, and is transparent in the NIR and SWIR bands.

[0037] While several exemplary embodiments have been shown and described, numerous variations and alternative embodiments will occur to those skilled in the art. Such variations and alternative embodiments are contemplated and can be made without departing from the scope of the invention as defined in the appended claims.

Claims

1. A water-based acrylic latex paint, an acrylic latex binder that is transparent in the NIR and SWIR bands; a solvent of water; a mixture of a deflocculated pigment transparent in the NIR and SWIR bands and a dispersant transparent in the NIR and SWIR bands, the mixture having a dispersant / pigment (DOP) ratio of 0.5 to 1.5; a rheology modifier; The water-based acrylic latex paint dries at ambient temperature and pressure to form a coating in which the deaggregated pigment has a low concentration and is highly dispersed throughout, absorbs in the visible band to produce color, and is transparent in the NIR and SWIR bands.

2. 2. The water-based acrylic latex paint of claim 1, wherein the visible band spans from 400 to 700 nm, the NIR band spans from 800 to 1300 nm, and the SWIR band spans from 1300 to 2200 nm.

3. 3. The water-based acrylic latex paint of claim 2, wherein the coating has an average transmission of less than 20% in the visible band, greater than 60% in the NIR band, and greater than 80% in the SWIR band.

4. 4. The water-based acrylic latex paint of claim 3, wherein the transmittance in the visible, NIR, and SWIR bands is controlled by the DOP ratio, the weight percentage of the deaggregated pigment in the water-based acrylic latex paint of 1-2%, and a coating thickness of 2-4 mils.

5. 5. The water-based acrylic latex paint of claim 4, wherein the DOP ratio is 0.8 to 1.

5.

6. 5. The water-based acrylic latex paint of claim 4, wherein the acrylic latex binder is RHOPLEX® AC-261F, the deflocculating pigment is Paliogen® Black L0086, the dispersant is EFKA® PX4310, and the DOP ratio is approximately 1.

7. 10. The water-based acrylic latex paint of claim 1, wherein the transmittance in the visible, NIR, and SWIR bands is controlled by the DOP ratio, the weight percentage of the deaggregated pigment in the water-based acrylic latex paint of 1-2%, and a coating thickness of 2-4 mils.

8. 8. The water-based acrylic latex paint of claim 7, wherein the DOP ratio is approximately 1.

9. 10. The water-based acrylic latex paint of claim 1, wherein said acrylic latex binder and said dispersant each have an average transmittance of at least 90% in the NIR and SWIR bands.

10. 10. The water-based acrylic latex paint of claim 1, wherein said dispersant has a molecular weight greater than 2,000 grams per mole.

11. 10. The water-based acrylic latex paint of claim 1, wherein the dispersant is an acrylate-based block copolymer containing amine-functional blocks for anchoring onto the deflocculating pigment.

12. 10. The water-based acrylic latex paint of claim 1, wherein the rheology modifier provides associative thickening to the water-based acrylic latex paint.

13. 13. The water-based acrylic latex paint of claim 12, wherein the rheology modifier is a hydrophobically modified alkali-soluble rheology modifier.

14. 10. The water-based acrylic latex paint of claim 1, wherein the deflocculated pigment has a cutoff wavelength between the visible and NIR bands.

15. 10. The water-based acrylic latex paint of claim 1, wherein the deflocculated pigment produces a black color.

16. 10. The water-based acrylic latex paint of claim 1 further comprising a second pigment to produce a color other than black.

17. 1. A method for formulating a water-based acrylic latex paint, comprising: premixing a pigment that is transparent in the NIR and SWIR bands with a dispersant that is transparent in the NIR and SWIR bands, wherein the mixture has a dispersant / pigment (DOP) ratio of 0.5 to 1.5; applying mechanical crushing energy to deagglomerate the pigment particles; mixing a solvent comprising water, an acrylic latex binder transparent in the NIR and SWIR bands, and a rheology modifier; The water-based acrylic latex paint dries at ambient temperature and pressure to form a coating in which the pigment has a low concentration and is highly dispersed throughout, absorbs in the visible band to produce color, and is transparent in the NIR and SWIR bands.

18. 18. The method of claim 17, wherein the transmittance in the visible, NIR, and SWIR bands is controlled by the DOP ratio, the weight percentage of the pigment in the water-based acrylic latex paint of 1-2%, and a coating thickness of 2-4 mils.

19. 18. The method of claim 17, wherein the dispersant is an acrylate-based block copolymer containing an amine-functional block having a molecular weight greater than 2,000 grams per mole.

20. An infrared transparent product, The product includes a body configured to cover a transmitting unit and a receiving unit of NIR and SWIR light rays in an IR sensor; The body includes: a substrate having transparency extending into the NIR and SWIR bands; a 2-4 mil thick coating on the rear or front surface of said substrate; The coating layer comprises: a water-based acrylic latex paint comprising a mixture of 2.6 to 5.2 wt. % deflocculated pigment and dispersant, the mixture being transparent in the NIR and SWIR bands, the dispersant / pigment (DOP) weight ratio being 0.5 to 1.5, and a rheology modifier; The water-based acrylic latex paint cures at ambient temperature and pressure to form the coating, wherein the deaggregated pigment has a low concentration and is highly dispersed throughout the coating, and the coating absorbs and produces color in the visible band and is transparent in the NIR and SWIR bands.

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