A waterborne radiation refrigeration coating for metal surfaces, a preparation method thereof and a coating layer

Abstract

The application discloses a water-based radiation refrigeration coating for metal surfaces, a preparation method thereof and a coating layer. The water-based radiation refrigeration coating for metal surfaces comprises: a two-component water-based epoxy anticorrosive primer, a two-component water-based acrylic polyurethane intermediate paint and a two-component water-based acrylic polyurethane topcoat. The application adopts a matching mode of the two-component water-based epoxy anticorrosive primer + the two-component water-based acrylic polyurethane intermediate paint + the two-component water-based acrylic polyurethane topcoat, which not only guarantees the anticorrosion of the coating layer, but also guarantees the high reflectivity, the radiation refrigeration effect and the good decoration of the coating layer, and can be widely used in the decoration and protection of metal surfaces of oil and gas storage tanks, transformer substations, ring network cabinets and cold chain transport vehicles and the like.

Description

Technical Field

[0001] This invention relates to the field of waterborne radiation cooling coating technology, and in particular to a waterborne radiation cooling coating for metal surfaces, its preparation method and coating. Background Technology

[0002] With industrial progress and the development of human society, the demand for cooling is increasing in both industrial production and daily applications. However, the widely used air conditioning system consumes a large amount of electricity and generates significant carbon emissions, exacerbating the greenhouse effect. To reduce carbon emissions, people have been striving to explore new, green, and environmentally friendly thermal management methods.

[0003] The Earth's atmosphere has varying transmittance for different electromagnetic waves. Wavelengths with higher transmittance are called "atmospheric windows," such as 0.3–2.5 μm, 3.2–4.8 μm, and 8–13 μm. Blackbody radiation at room temperature is primarily concentrated in the 8–13 μm band. Utilizing this characteristic, objects on Earth can cool themselves by radiative heat exchange, releasing their heat into the absolute zero space of outer space in the form of electromagnetic waves in the 8–13 μm band. This method of releasing heat entirely through radiation into space is commonly referred to as radiative cooling. Radiative cooling has attracted widespread attention from researchers both domestically and internationally due to its advantage of requiring no energy consumption. To achieve a cooling effect, materials need high transmittance in the atmospheric window bands to dissipate heat, or high emissivity to radiate heat and reflect sunlight. An ideal radiator is a selective radiator, with a spectral characteristic of having a reflectivity of 1 outside the 8–13 μm band and an emissivity of 1 within the 8–13 μm band.

[0004] Currently, radiative cooling technology, as a zero-energy building air conditioning method, has experienced rapid development and demonstrated significant practical value. However, existing radiative cooling technology is mainly applied to architectural coatings on concrete surfaces, with very little research on its application to metal surfaces. Metal surface coating systems have higher requirements for corrosion resistance and better decorative properties, which differ somewhat from the corrosion protection systems for concrete surfaces. Therefore, research on water-based radiative cooling coating systems for metal surfaces is of great significance. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned technical deficiencies and to propose a water-based radiation cooling coating for metal surfaces, its preparation method and coating, thereby solving the technical problem that existing coatings applied to metal surfaces cannot simultaneously achieve good corrosion resistance, decoration and radiation cooling effect.

[0006] In a first aspect, the present invention provides a water-based radiation cooling coating for metal surfaces, comprising: a two-component water-based epoxy anti-corrosion primer, a two-component water-based acrylic polyurethane intermediate coat, and a two-component water-based acrylic polyurethane topcoat; wherein...

[0007] The two-component waterborne epoxy anti-corrosion primer comprises: component A1 and component B1; assuming the total of components A1 and B1 is 100%, component A1 includes: 30%–40% waterborne epoxy emulsion, 1%–1.6% wetting and dispersing agent, 1%–5% organic bentonite slurry (2%–4% by mass), 0.2%–0.5% defoamer, 0.4%–0.8% polyurethane rheology modifier, 5%–8% rutile titanium dioxide, and metal oxide... The composition includes: 1%–3% mixed-phase pigment, 2%–5% mica powder, 6%–10% finely precipitated barium sulfate, 3%–6% anti-rust pigment, 0.3%–0.8% film-forming aid, 0.2%–0.4% substrate wetting agent, and 10%–20% deionized water; Component B1 includes: 10%–15% water-based epoxy curing agent, 0.3%–0.5% film-forming aid, 0.1%–0.5% anti-flash rust agent, and 10%–15% deionized water.

[0008] The two-component waterborne acrylic polyurethane intermediate paint comprises: component A2 and component B2; with the total of components A2 and B2 being 100%, component A2 includes: 38%–45% waterborne hydroxyl acrylic dispersion, 0.8%–1.2% wetting and dispersing agent, 1%–5% organic bentonite slurry (2%–4% by mass), 0.4%–0.8% polyurethane rheology modifier, 5%–8% film-forming aid, and 0.3%–0.7% defoamer. The components are: rutile titanium dioxide 6%–10%, finely precipitated barium sulfate 7%–11%, silica aerogel 1%–3%, hollow glass microspheres 6%–12%, pH adjuster 0.1%–0.3%, substrate wetting agent 0.2%–0.4%, bactericide and preservative 0.1%–0.2%, deionized water 5%–20%; Component B2 includes: aqueous isocyanate curing agent 8%–15%, propylene glycol diacetate 2%–4%.

[0009] The two-component waterborne acrylic polyurethane topcoat includes component A3 and component B3. Taking the total of components A3 and B3 as 100%, component A3 includes: 45%–55% waterborne hydroxyl acrylic dispersion, 0.8%–1.2% wetting and dispersing agent, 1%–5% organic bentonite slurry (2%–4% by mass), 0.4%–0.8% polyurethane rheology modifier, 5%–8% film-forming aid, 0.3%–0.7% defoamer, 20%–25% infrared reflective titanium dioxide, 0.1%–0.3% pH adjuster, 0.2%–0.4% substrate wetting agent, 0.2%–0.4% leveling agent, 0.1%–0.2% bactericide and preservative, and 1%–10% deionized water. Component B3 includes: 8%–15% waterborne isocyanate curing agent and 2%–4% propylene glycol diacetate.

[0010] Secondly, the present invention provides a method for preparing a water-based radiation cooling coating for a metal surface, comprising the following steps:

[0011] Preparation of a two-component waterborne epoxy anti-corrosion primer;

[0012] Preparation of a two-component waterborne acrylic polyurethane intermediate varnish;

[0013] Preparation of a two-component waterborne acrylic polyurethane topcoat; wherein,

[0014] The preparation steps of the above-mentioned two-component waterborne epoxy anti-corrosion primer include:

[0015] Under low-speed stirring, a portion of deionized water, wetting and dispersing agent, a portion of defoamer, organic bentonite slurry, and film-forming aid are dispersed evenly to obtain a first mixture. Under low-speed stirring, rutile titanium dioxide, metal oxide mixed-phase pigments, rust-preventing pigments, mica powder, and finely precipitated barium sulfate are added to the first mixture. After high-speed dispersion, the mixture is ground until the slurry fineness is ≤30μm to obtain a second mixture. Under low-speed stirring, an aqueous epoxy emulsion, substrate wetting agent, the remaining defoamer, polyurethane rheology modifier, and the remaining deionized water are added to the second mixture and dispersed evenly to obtain component A1.

[0016] Deionized water, film-forming aid, and anti-flash rust aid were added to the water-based epoxy curing agent under low-speed stirring and dispersed evenly to obtain component B1;

[0017] The preparation steps of the above two-component waterborne acrylic polyurethane intermediate varnish include:

[0018] Under low-speed stirring, the aqueous hydroxy acrylic dispersion, wetting and dispersing agent, part of the defoamer, organic bentonite slurry, film-forming aid, pH adjuster, and bactericide and preservative are dispersed evenly to obtain a first mixture. Under low-speed stirring, silica aerogel is added to the first mixture and dispersed evenly at high speed to obtain a second mixture. Under low-speed stirring, rutile titanium dioxide and finely precipitated barium sulfate are added to the second mixture and dispersed evenly at high speed to obtain a third mixture. Under low-speed stirring, the remaining defoamer, substrate wetting agent, polyurethane rheology modifier, and part of deionized water are added to the third mixture and dispersed evenly to obtain a fourth mixture. Under low-speed stirring, hollow glass microspheres and the remaining deionized water are added to the fourth mixture and dispersed evenly to obtain component A2.

[0019] The film-forming aid was added to the aqueous isocyanate curing agent and dispersed evenly under low-speed stirring to obtain component B2.

[0020] The preparation steps of the above two-component waterborne acrylic polyurethane topcoat include:

[0021] Under low-speed stirring, the aqueous hydroxy acrylic dispersion, wetting and dispersing agent, part of the defoamer, organic bentonite slurry, film-forming aid, pH adjuster, and bactericide and preservative are dispersed evenly to obtain a first mixture; infrared reflective titanium dioxide is added to the first mixture under low-speed stirring and dispersed evenly to obtain a second mixture; the remaining defoamer, substrate wetting agent, polyurethane rheology modifier, leveling agent, and deionized water are added to the second mixture under low-speed stirring and dispersed evenly to obtain component A3;

[0022] The film-forming aid was added to the water-based isocyanate curing agent and dispersed evenly under low-speed stirring to obtain component B3.

[0023] Thirdly, the present invention provides a water-based radiation cooling coating for a metal surface, comprising: a two-component water-based epoxy anti-corrosion primer, a two-component water-based acrylic polyurethane intermediate coating, and a two-component water-based acrylic polyurethane topcoat; wherein...

[0024] The above-mentioned two-component waterborne epoxy anti-corrosion primer is formed by curing the two-component waterborne epoxy anti-corrosion primer provided in the first aspect of the present invention;

[0025] The above-mentioned two-component waterborne acrylic polyurethane intermediate coating is formed by curing the two-component waterborne acrylic polyurethane intermediate paint provided in the first aspect of the present invention.

[0026] The above-mentioned two-component waterborne acrylic polyurethane topcoat is formed by curing the two-component waterborne acrylic polyurethane topcoat provided in the first aspect of the present invention.

[0027] Compared with the prior art, the beneficial effects of the present invention include:

[0028] The water-based radiation cooling coating for metal surfaces of the present invention has good corrosion resistance, radiation cooling effect and decorative properties, and can be widely used for decoration and protection of metal surfaces such as oil and gas storage tanks, substations, ring main units and cold chain transport vehicles. Attached Figure Description

[0029] Figure 1 This is a comparison chart of the reflectance values ​​of coatings prepared using different pigments;

[0030] Figure 2 This is a comparison chart of the reflectance values ​​of coatings prepared using different titanium dioxide powders;

[0031] Figure 3 This is a graph showing the effect of white topcoat film thickness on reflectivity;

[0032] Figure 4 This is a reflection value diagram of coating system 1. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0034] To achieve high reflectivity and radiative cooling effects in coatings, the most crucial aspects of primers, intermediate coats, and topcoats, beyond meeting the basic performance requirements of a coating, are high reflectivity and radiative cooling performance. The selection of pigments and fillers is paramount, followed by the choice of film-forming substances. The synergistic effect among primers, intermediate coats, and topcoats is also vital; any choice of pigments or fillers that reduces coating reflectivity will lead to a decrease in the reflectivity, corrosion resistance, or decorative properties of the coating system. Therefore, providing a water-based radiative cooling coating system suitable for metal surfaces that balances good corrosion resistance, decorative properties, and radiative cooling effects presents significant challenges.

[0035] Based on this, the present invention is proposed.

[0036] In a first aspect, the present invention provides a water-based radiation cooling coating for metal surfaces, comprising: a two-component water-based epoxy anti-corrosion primer, a two-component water-based acrylic polyurethane intermediate coat, and a two-component water-based acrylic polyurethane topcoat.

[0037] In this embodiment, the two-component waterborne epoxy anti-corrosion primer includes: component A1 and component B1; wherein, taking the sum of components A1 and B1 as 100%, component A1 includes: 30%–40% waterborne epoxy emulsion, 1%–1.6% wetting and dispersing agent, 1%–5% organic bentonite slurry, 0.2%–0.5% defoamer, 0.4%–0.8% polyurethane rheology modifier, 5%–8% rutile titanium dioxide, and metal oxide... The composition includes: 1%–3% mixed-phase pigment, 2%–5% mica powder, 6%–10% finely precipitated barium sulfate, 3%–6% anti-rust pigment, 0.3%–0.8% film-forming aid, 0.2%–0.4% substrate wetting agent, and 10%–20% deionized water; Component B1 includes: 10%–15% water-based epoxy curing agent, 0.3%–0.5% film-forming aid, 0.1%–0.5% anti-flash rust aid, and 10%–15% deionized water.

[0038] This two-component waterborne epoxy anti-corrosion primer is formulated with waterborne epoxy emulsion and waterborne epoxy curing agent as film-forming substances, rutile titanium dioxide and metal oxide mixed-phase pigments as pigments, finely precipitated barium sulfate powder and mica powder as fillers, and supplemented with anti-rust pigments, additives and deionized water. It has excellent anti-corrosion performance, high reflectivity and radiative cooling effect.

[0039] In this embodiment, the two-component waterborne acrylic polyurethane intermediate paint comprises: component A2 and component B2; wherein, with the total of components A2 and B2 being 100%, component A2 comprises: 38%–45% waterborne hydroxyl acrylic dispersion, 0.8%–1.2% wetting and dispersing agent, 1%–5% organic bentonite slurry, 0.4%–0.8% polyurethane rheology modifier, 5%–8% film-forming aid, and 0.3%–0.7% defoamer. The components are: rutile titanium dioxide 6%–10%, finely precipitated barium sulfate 7%–11%, silica aerogel 1%–3%, hollow glass microspheres 6%–12%, pH adjuster 0.1%–0.3%, substrate wetting agent 0.2%–0.4%, bactericide and preservative 0.1%–0.2%, and deionized water 5%–20%; component B2 includes: aqueous isocyanate curing agent 8%–15%, and propylene glycol diacetate 2%–4%.

[0040] This two-component waterborne acrylic polyurethane intermediate paint uses waterborne hydroxyl acrylic dispersion and waterborne isocyanate curing agent as film-forming substances, and rutile titanium dioxide, hollow glass microspheres, and silica aerogel as reflective radiation cooling fillers. The composite use of silica aerogel and hollow glass microspheres significantly reduces thermal conductivity and improves radiation cooling effect. The introduction of rutile titanium dioxide provides both masking and reflective properties. Simultaneously, finely precipitated barium sulfate is used as a bulk filler, supplemented with additives and deionized water, resulting in high reflective radiation cooling performance. Compared with existing intermediate paints, the intermediate paint of this invention can achieve a higher coating thickness with the same number of coats, thereby increasing the film thickness of the coating system, while also offering higher cost-effectiveness.

[0041] In this embodiment, the two-component waterborne acrylic polyurethane topcoat includes: component A3 and component B3; wherein, taking the sum of components A3 and B3 as 100%, component A3 includes: 45%–55% waterborne hydroxy acrylic dispersion, 0.8%–1.2% wetting and dispersing agent, 1%–5% organic bentonite slurry, 0.4%–0.8% polyurethane rheology modifier, 5%–8% film-forming aid, 0.3%–0.7% defoamer, 20%–25% infrared reflective titanium dioxide, 0.1%–0.3% pH adjuster, 0.2%–0.4% substrate wetting agent, 0.2%–0.4% leveling agent, 0.1%–0.2% bactericide and preservative, and 1%–10% deionized water; component B3 includes: 8%–15% waterborne isocyanate curing agent and 2%–4% propylene glycol diacetate.

[0042] This two-component waterborne acrylic polyurethane topcoat is formulated with waterborne hydroxy acrylic dispersion and waterborne isocyanate curing agent as film-forming substances, rutile titanium dioxide as a radiation-reflecting and cooling substance, and supplemented with additives and deionized water. It has high reflectivity, weather resistance, stain resistance, gloss and gloss retention.

[0043] This invention enables the preparation of water-based radiation cooling coatings for metal surfaces by using materials with high solar reflectivity, high emissivity, and low thermal conductivity.

[0044] This invention employs a two-component waterborne epoxy anti-corrosion primer, a two-component waterborne acrylic polyurethane intermediate coat, and a two-component waterborne acrylic polyurethane topcoat. This combination ensures the coating's anti-corrosion properties, high reflectivity, radiative cooling effect, and good decorative properties.

[0045] Furthermore, the waterborne epoxy emulsion is a "Type 1" solid epoxy resin emulsion. Metal coatings made from "Type 1" solid epoxy resin emulsions exhibit characteristics such as fast drying time, good adhesion, flexibility, and corrosion resistance. When combined with a waterborne epoxy curing agent, they can be formulated into coatings with low volatile organic compound (VOC) content, long pot life, good chemical resistance, and excellent anti-corrosion properties. Even further, the waterborne epoxy emulsion has a solid content of 50%–60% by mass. This invention does not limit the type of "Type 1" solid epoxy resin emulsion; for example, it can be Araldite PZ3961-1, etc.

[0046] Furthermore, the waterborne epoxy curing agent is at least one of modified aliphatic amines or modified polyamides. Even further, the waterborne epoxy curing agent has a solids content of 35% to 45% by weight.

[0047] Furthermore, the hydroxyl content of the waterborne hydroxyl acrylic dispersion is 3%–4%. This waterborne hydroxyl acrylic dispersion exhibits excellent gloss, hardness, and fullness, as well as outstanding chemical resistance and good gloss retention and weather resistance. Combined with a hydrophilic aliphatic polyisocyanate curing agent based on 1,6-methylene diisocyanate (HDI) that exhibits good anti-yellowing and weather resistance, the prepared polyurethane coating film possesses excellent gloss retention, color retention, and anti-yellowing properties, and is widely used for corrosion protection of outdoor metal surfaces. Even further, the waterborne hydroxyl acrylic dispersion has a solids content of 40%–60% by weight.

[0048] Furthermore, the waterborne isocyanate curing agent is a waterborne aliphatic isocyanate curing agent, and even further, it is a hydrophilic aliphatic polyisocyanate curing agent based on 1,6-methylene diisocyanate (HDI). Even further, the waterborne isocyanate curing agent has a solids content of >99% by mass.

[0049] Furthermore, the rust-inhibiting pigment is strontium zinc phosphosilicate. This rust-inhibiting pigment is a white, general-purpose corrosion inhibitor that can be used in protective and anti-corrosion coatings for various resin systems.

[0050] Furthermore, the metal oxide mixed-phase pigment is at least one of zinc iron yellow, medium chrome yellow, titanium chrome brown, and titanium nickel yellow, preferably zinc iron yellow. This metal oxide mixed-phase pigment is an infrared reflective pigment with excellent lightfastness, weather resistance, heat resistance, acid and alkali resistance, and chemical corrosion resistance. It does not bleed, does not migrate, is easily dispersed, and has good hiding power. It is an internationally recognized non-toxic and environmentally friendly pigment, suitable for coloring applications requiring high ultraviolet reflectivity.

[0051] Furthermore, the rutile titanium dioxide is rutile titanium dioxide coated with inorganic substances such as zirconium aluminum. This rutile titanium dioxide exhibits excellent weather resistance, superior optical properties, and high reflectivity. This invention does not limit the specific type of rutile titanium dioxide; those skilled in the art can select it according to actual conditions. For example, the rutile titanium dioxide can be BLR-699, etc.

[0052] Furthermore, infrared-reflecting titanium dioxide is available in W550 and IR-1000. Infrared-reflecting titanium dioxide is a rutile titanium dioxide pigment that reflects near-infrared light. By altering solar reflection through crystal size, it produces enhanced solar reflective properties across a wide color range. Larger crystal sizes change the reflection focus across the entire solar spectrum. Compared to ordinary titanium dioxide, this crystal ensures the reflection of a larger proportion of near-infrared light while maintaining extremely important hiding power and tinting strength.

[0053] In this invention, adding too much titanium dioxide increases the cost, but the reflectivity is the same for the same film thickness; adding too little mainly affects the hiding power of the coating, but has little effect on the reflectivity.

[0054] Furthermore, silica aerogel is the world's least dense solid, with over 95% (by volume) of its micropowder structure being air. Its pore size is smaller than the mean free path of air molecules at normal pressure, so air molecules are nearly stationary within the aerogel pores, thus avoiding convective heat transfer. The aerogel's extremely low bulk density and the tortuous paths of its nano-network structure also prevent heat conduction between the gaseous and solid states, and the nearly infinite number of pore walls minimizes thermal radiation. These three factors work together to almost completely block all heat transfer pathways, giving aerogel an insulation effect unmatched by other materials. This nanoporous material with high specific surface area, high porosity, low density, and extremely low thermal conductivity possesses excellent thermal insulation, heat preservation, fireproofing, waterproofing, sound insulation, and shock resistance properties.

[0055] Furthermore, hollow glass microspheres are micron-sized, smooth-surfaced hollow glass microspheres that appear as hollow, transparent spheres under a microscope. They possess a variety of properties, including low density, high strength, low thermal conductivity, electrical insulation, high temperature resistance, and acid and alkali resistance. They also exhibit good flowability and chemical stability. Their applications enable the performance upgrading and optimization of various materials and are of significant strategic importance for material lightweighting and energy conservation and emission reduction.

[0056] Furthermore, the mass fraction of the organic bentonite slurry is 2% to 4%.

[0057] In some specific embodiments of the present invention, the preparation method of the organic bentonite slurry is as follows: An organic bentonite rheology modifier is added to water, and after sufficient hydration, a bactericide and preservative are added and mixed evenly. The bactericide and preservative constitute 0.1% to 0.2% of the mass of deionized water.

[0058] In this invention, organic bentonite rheology modifiers or polyurethane rheology modifiers are used to improve the rheological properties of the system. Because powders such as titanium dioxide, rust-preventive pigments, and finely precipitated barium sulfate have high density and are prone to settling, appropriate amounts of rheology modifiers are added to the intermediate and topcoat formulations to improve the system's rheological properties. Organic bentonite rheology modifiers, in addition to their high-efficiency thickening, viscosity thermal stability, and thixotropic properties, also possess electrolyte stability, emulsion stability, prevention of hard precipitation of pigments or fillers, reduction of moisture shrinkage, and prevention of color separation and blooming phenomena. Polyurethane rheology modifiers have a special "oleophilic-hydrophilic-oleophilic" triblock polymer structure, exhibiting excellent stabilizing effects. This invention, through the combined use of two rheology modifiers, ensures both the rheological properties of the coating and good application performance.

[0059] Furthermore, the film-forming aid is at least one selected from ethylene glycol butyl ether, dipropylene glycol monomethyl ether, dipropylene glycol butyl ether, and propylene glycol diacetate. By selecting the above-mentioned film-forming aids with different boiling points, the present invention can ensure both the dryness of the coating film and good film-forming and leveling properties.

[0060] Furthermore, the wetting and dispersing agent is a high molecular weight block copolymer. Aqueous systems exhibit poor wetting of pigments, therefore an appropriate amount of dispersant needs to be added. The high molecular weight dispersant, through steric hindrance, deflocculates inorganic and organic pigments, thereby achieving high gloss, enhanced color intensity, improved leveling properties, and increased pigment content. This invention does not limit the specific type of wetting and dispersing agent; those skilled in the art can select one according to actual conditions. For example, the wetting and dispersing agent can be DISPERBYK-190, DISPERBYK-2012, etc.

[0061] Furthermore, the substrate wetting agent is a polyether siloxane copolymer. This substrate wetting agent exhibits high performance, excellent anti-cratering effect, and good recoatability. This invention does not limit the specific type of substrate wetting agent; those skilled in the art can select it according to actual conditions. For example, the substrate wetting agent can be TEGO Wet 270, etc.

[0062] Furthermore, the defoamer is an organosilicon defoamer or defoaming agent. This defoamer exhibits good compatibility with water-based hydroxy acrylic dispersions while effectively eliminating large and micro bubbles in the coating. This invention does not limit the specific type of defoamer; those skilled in the art can select one according to actual conditions. For example, the defoamer can be… Airex902 W, BYK-028, etc.

[0063] Furthermore, the leveling agent is a polyether-modified silicone leveling agent. This leveling agent has low surface tension and anti-cratering ability, which can increase the lubricity, surface smoothness, and gloss of the substrate. This invention does not limit the specific type of leveling agent; those skilled in the art can select one according to actual conditions. For example, the leveling agent can be BYK-333, etc.

[0064] Furthermore, the flash rust inhibitor is an organic, bio-based liquid corrosion inhibitor that can prevent flash rust in all types of water-based wet coatings, thereby eliminating flash rust on ferrous metals during the coating drying process. This invention does not limit the specific type of flash rust inhibitor; those skilled in the art can select one according to actual conditions. For example, the flash rust inhibitor can be... H10, etc.

[0065] Furthermore, the pH adjuster is an organic amine, preferably dimethylethanolamine. This invention ensures the stability of the coating system by adjusting its pH value.

[0066] Furthermore, the bactericide and preservative is an organic, highly efficient, and low-toxicity bactericide and preservative, suitable for polymer emulsions, pigment pastes, and various water-based coatings. This invention does not limit the specific type of bactericide and preservative; those skilled in the art can select one according to actual conditions. For example, the bactericide and preservative can be… LEX, etc.

[0067] In this embodiment, the mass ratio of component A1 to component B1 is (3-4):1; the mass ratio of component A2 to component B2 is (7-9):1; and the mass ratio of component A3 to component B3 is (5-7):1.

[0068] Secondly, the present invention provides a method for preparing a water-based radiation cooling coating for metal surfaces, comprising the following steps: S1, preparation of a two-component water-based epoxy anti-corrosion primer; S2, preparation of a two-component water-based acrylic polyurethane intermediate coat; S3, preparation of a two-component water-based acrylic polyurethane topcoat.

[0069] In this embodiment, the preparation steps of the above-mentioned two-component waterborne epoxy anti-corrosion primer include:

[0070] S11. Under low-speed stirring, a portion of deionized water, wetting and dispersing agent, a portion of defoamer, organic bentonite slurry, and film-forming aid are dispersed evenly to obtain a first mixture. Under low-speed stirring, rutile titanium dioxide, metal oxide mixed-phase pigment, anti-rust pigment, mica powder, and finely precipitated barium sulfate are added to the first mixture. After high-speed dispersion, the mixture is ground until the slurry fineness is ≤30μm to obtain a second mixture. Under low-speed stirring, aqueous epoxy emulsion, substrate wetting agent, the remaining defoamer, polyurethane rheology modifier, and the remaining deionized water are added to the second mixture and dispersed evenly to obtain component A1.

[0071] S12. Under low-speed stirring, deionized water, film-forming aid, and anti-flash rust aid are added to the water-based epoxy curing agent and dispersed evenly to obtain component B1.

[0072] In this embodiment, the preparation steps of the above-mentioned two-component waterborne acrylic polyurethane intermediate paint include:

[0073] S21. Under low-speed stirring, the aqueous hydroxy acrylic dispersion, wetting and dispersing agent, part of the defoamer, organic bentonite slurry, film-forming aid, pH adjuster, and bactericide and preservative are dispersed evenly to obtain a first mixture; under low-speed stirring, silica aerogel is added to the first mixture and dispersed evenly at high speed to obtain a second mixture; under low-speed stirring, rutile titanium dioxide and finely precipitated barium sulfate are added to the second mixture and dispersed evenly at high speed to obtain a third mixture; under low-speed stirring, the remaining defoamer, substrate wetting agent, polyurethane rheology modifier, and part of deionized water are added to the third mixture and dispersed evenly to obtain a fourth mixture; under low-speed stirring, hollow glass microspheres and the remaining deionized water are added to the fourth mixture and dispersed evenly to obtain component A2;

[0074] S22. Under low-speed stirring, the film-forming aid is added to the water-based isocyanate curing agent and dispersed evenly to obtain component B2.

[0075] In this embodiment, the preparation steps of the above-mentioned two-component waterborne acrylic polyurethane topcoat include:

[0076] S31. Under low-speed stirring, the aqueous hydroxy acrylic dispersion, wetting and dispersing agent, part of the defoamer, organic bentonite slurry, film-forming aid, pH adjuster, and bactericide and preservative are dispersed evenly to obtain a first mixture; under low-speed stirring, infrared reflective titanium dioxide is added to the first mixture and dispersed evenly at high speed to obtain a second mixture; under low-speed stirring, the remaining defoamer, substrate wetting agent, polyurethane rheology modifier, leveling agent, and deionized water are added to the second mixture and dispersed evenly to obtain component A3;

[0077] S32. Under low-speed stirring, the film-forming aid is added to the water-based isocyanate curing agent and dispersed evenly to obtain component B3.

[0078] Furthermore, the deionized water comprises 80% to 90% of the total deionized water mass; the defoamer comprises 40% to 60% of the total defoamer mass.

[0079] Furthermore, the low-speed stirring speed is 500–1000 r / min, and the stirring time is 15–25 min; the high-speed dispersion speed is 2000–2500 r / min, and the stirring time is 30–40 min.

[0080] Thirdly, the present invention provides a water-based radiation cooling coating for a metal surface, comprising: a two-component water-based epoxy anti-corrosion primer, a two-component water-based acrylic polyurethane intermediate coating, and a two-component water-based acrylic polyurethane topcoat; wherein...

[0081] The above-mentioned two-component waterborne epoxy anti-corrosion primer is formed by curing the two-component waterborne epoxy anti-corrosion primer provided in the first aspect of the present invention;

[0082] The above-mentioned two-component waterborne acrylic polyurethane intermediate coating is formed by curing the two-component waterborne acrylic polyurethane intermediate paint provided in the first aspect of the present invention.

[0083] The above-mentioned two-component waterborne acrylic polyurethane topcoat is formed by curing the two-component waterborne acrylic polyurethane topcoat provided in the first aspect of the present invention.

[0084] In this embodiment, the thickness of the two-component waterborne epoxy anti-corrosion primer is 70-90 μm, the thickness of the two-component waterborne acrylic polyurethane intermediate coating is 280-320 μm, and the thickness of the two-component waterborne acrylic polyurethane topcoat is 70-90 μm.

[0085] In this embodiment, the two-component coatings need to be mixed evenly before coating, and then left to stand for 10 to 20 minutes.

[0086] In this embodiment, the coating can be cured at room temperature or by baking.

[0087] In this embodiment, the metal to be coated needs to be pretreated before coating. Further, the pretreatment steps are as follows: clean the oil, rust, and old paint from the surface of the metal to be coated, and keep it clean; sandblast or shot blast to Sa2.5 grade; and remove welding slag, spatter, and grind smooth the welded, cut, or burned areas.

[0088] To avoid redundancy, the raw materials used in the following embodiments and comparative examples of this invention are summarized as follows:

[0089] Aquatic epoxy emulsion Araldite PZ3961-1, with a solid content of 53±1% by weight; Aquatic epoxy curing agent Aradur3986, with a solid content of 40±1% by weight; Aquatic hydroxy acrylic dispersion AQUAPAC-8300, with a solid content of 45±1% by weight; Aquatic isocyanate curing agent AQUAPU-298, with a solid content of >99% by weight.

[0090] The rutile titanium dioxide is BLR-699, the infrared reflective pigments are W550 and IR-1000 titanium dioxide, the metal oxide mixed phase pigment is zinc iron yellow, the anti-rust pigment is SZP-391, the mica powder is CJ-A5, the silica aerogel is AG-D, and the hollow glass microspheres are HL38.

[0091] The rheology modifiers are BENTONE LT organobentonite rheology modifier, ACRYSOL RM-8W and ACRYSOL RM-2020NPR polyurethane rheology modifiers, and the defoamer is... Airex902 W and BYK-028, wetting and dispersing agents are DISPERBYK-190 and DISPERBYK-2012, film-forming aids are ethylene glycol butyl ether, dipropylene glycol monomethyl ether, dipropylene glycol butyl ether and propylene glycol diacetate, substrate wetting agent is TEGO Wet 270, and bactericide and preservative are... LEX, pH adjuster is dimethylethanolamine, flash rust inhibitor is... H10, leveling agent is BYK-333.

[0092] The preparation method of the 3wt% organic bentonite slurry used in this invention is as follows: weigh each component according to the proportion, add BENTONE LT to water at a speed of 500-800 r / min, disperse at high speed for 15-20 min at a speed of 2000-2500 r / min, and after sufficient hydration, add 0.1% of the deionized water mass of bactericide and preservative and mix evenly.

[0093] The water-based radiation cooling coating system for metal surfaces includes: a two-component water-based epoxy anti-corrosion primer, a two-component water-based acrylic polyurethane intermediate coat, and a two-component water-based acrylic polyurethane topcoat. The mass percentage of each component and its preparation method are as follows:

[0094] For ease of comparison, the mass percentage of each component in Group 11 and Group 12 of the two-component waterborne epoxy anticorrosive primer is summarized in Table 1 below.

[0095] Table 1 Raw material dosage for different two-component waterborne epoxy anti-corrosion primer formulations

[0096]

[0097]

[0098] Preparation steps of component A1 of the two-component waterborne epoxy anti-corrosion primer:

[0099] (1) Weigh each component according to the mass ratio;

[0100] (2) Disperse the deionized water (80% of the total amount of A1 deionized water), wetting and dispersing agent, defoamer 1, organic bentonite slurry and film-forming aid evenly at a rotation speed of 500-1000 r / min to obtain the first mixture.

[0101] (3) Add rutile titanium dioxide, metal oxide mixed phase pigment or iron oxide yellow, anti-rust pigment, mica powder and fine precipitated barium sulfate to the first mixture at a speed of 500-1000 r / min. Disperse at a high speed of 2000-2500 r / min for 15-25 min, and then grind until the slurry fineness is ≤30 μm to obtain the second mixture.

[0102] (4) Add waterborne epoxy emulsion, substrate wetting agent, defoamer 2, polyurethane rheology modifier and the balance deionized water to the second mixture at a speed of 500-1000 r / min. After uniform dispersion, the two-component waterborne epoxy anti-corrosion primer A1 component is obtained.

[0103] Preparation steps of component B1 of two-component waterborne epoxy anti-corrosion primer:

[0104] (1) Weigh each component according to the mass ratio;

[0105] (2) Deionized water, film-forming aid and anti-flash rust aid are added to waterborne epoxy curing agent at a speed of 500-1000 r / min and dispersed evenly to obtain two-component waterborne epoxy anti-corrosion primer B1 component.

[0106] For ease of comparison, the mass percentage content of each component in groups 21, 22, and 23 of the two-component waterborne acrylic polyurethane intermediate paint is summarized in Table 2 below.

[0107] Table 2 Raw material dosage for different two-component waterborne acrylic polyurethane intermediate paint formulations

[0108]

[0109]

[0110] Preparation steps of component A2 of two-component waterborne acrylic polyurethane intermediate paint:

[0111] (1) Weigh each component according to the mass ratio;

[0112] (2) The aqueous hydroxy acrylic acid dispersion, wetting and dispersing agent, defoamer 1, organic bentonite slurry, film-forming aid, pH adjuster and bactericide and preservative are evenly dispersed at a speed of 500-1000 r / min to obtain the first mixture.

[0113] (3) Add silica aerogel to the first mixture at a speed of 500-1000 r / min, and disperse at a speed of 2000-2500 r / min for 30-40 min to obtain the second mixture;

[0114] (4) Add rutile titanium dioxide and finely precipitated barium sulfate to the second mixture at a speed of 500-1000 r / min and disperse at a speed of 2000-2500 r / min for 30-40 min to obtain the third mixture;

[0115] (5) Add defoamer 2, substrate wetting agent, polyurethane rheology modifier and 90% of the total deionized water in A2 to the third mixture at a speed of 500-1000 r / min, and disperse evenly to obtain the fourth mixture.

[0116] (6) Hollow glass microspheres and the remainder deionized water were added to the fourth mixture at a speed of 500-1000 r / min. After being dispersed evenly, the two-component waterborne acrylic polyurethane intermediate paint A2 component was obtained.

[0117] Preparation steps of component B2 of two-component waterborne acrylic polyurethane intermediate varnish:

[0118] (1) Weigh each component according to the mass ratio;

[0119] (2) The film-forming aid is added to the waterborne isocyanate curing agent and dispersed evenly at a rotation speed of 500-1000 r / min to obtain the B component of the two-component waterborne acrylic polyurethane intermediate paint.

[0120] For ease of comparison, the mass percentage of each component in groups 31 to 34 of different two-component waterborne acrylic polyurethane topcoats is summarized in Table 3 below.

[0121] Table 3 Raw material dosage for different two-component waterborne acrylic polyurethane topcoat formulations

[0122]

[0123]

[0124] Two-component waterborne acrylic polyurethane topcoat includes the following steps:

[0125] Preparation steps of component A3 of two-component waterborne acrylic polyurethane topcoat:

[0126] (1) Weigh each component according to the mass ratio;

[0127] (2) The aqueous hydroxy acrylic acid dispersion, wetting and dispersing agent, defoamer 1, organic bentonite slurry, film-forming aid, pH adjuster and bactericide and preservative are evenly dispersed at a speed of 500-1000 r / min to obtain the first mixture.

[0128] (3) Add titanium dioxide to the first mixture at a speed of 500-1000 r / min and disperse it at a speed of 2000-2500 r / min for 30-40 min to obtain the second mixture;

[0129] (4) Add defoamer 2, substrate wetting agent, polyurethane rheology modifier, leveling agent and deionized water to the second mixture at a speed of 500-1000 r / min. After uniform dispersion, the two-component waterborne acrylic polyurethane topcoat A3 component is obtained.

[0130] It should be noted that the silica aerogel and hollow glass microspheres in group 33 are added in the same way as in group A2.

[0131] The preparation steps for component B3 of the two-component waterborne acrylic polyurethane topcoat are the same as those for component B2 of the two-component waterborne acrylic polyurethane intermediate coat.

[0132] Performance testing

[0133] (1) Performance testing of two-component waterborne epoxy anti-corrosion primer The reflectance of the coatings prepared using two-component waterborne epoxy anti-corrosion primers (groups 11 and 12) was tested and the results are shown in [Figure 1]. Figure 1 .

[0134] Depend on Figure 1 It is known that, for the same resin and filler system, the reflectivity of the coating film varies significantly depending on the pigment used, indicating that pigment is a crucial factor affecting coating reflectivity. The zinc-iron yellow pigment used in this invention produces coating films with high reflectivity. Similar to this pigment, coating films prepared with yellow pigments such as medium chrome yellow, titanium chrome brown, and titanium nickel yellow also have high reflectivity. However, the reflectivity of coating films prepared with iron oxide pigments such as iron oxide red, iron oxide black, iron oxide violet, and iron oxide brown is far lower than that of coating films prepared with zinc-iron yellow pigment. It is worth noting that when carbon black is used as a black pigment, because it primarily absorbs light, even a small amount of carbon black will result in an overall reflectivity of the coating film of <6%. Therefore, the reflectivity of a two-component waterborne epoxy zinc-rich primer coating film, which has good anti-corrosion properties, is also far lower than that of a coating film prepared with zinc-iron yellow pigment. Although the reflectance values ​​of the coatings prepared by these two different yellow pigments differ significantly, the general properties of the coatings are basically the same. If iron oxide yellow S313 is used to prepare the coating, the overall reflectance of the system will be reduced. Therefore, the primer prepared by the infrared reflective pigment zinc iron yellow has both high reflectance and good anti-corrosion performance.

[0135] (2) Performance testing of two-component waterborne acrylic polyurethane intermediate varnish The coatings prepared using two-component waterborne acrylic polyurethane intermediate paints (groups 21, 22, and 23) were sprayed and their performance was tested.

[0136] Table 4

[0137]

[0138] As shown in Table 4, hollow glass microspheres are a smooth, white, free-flowing powder with a true density of 0.37–0.39 g / cm³. 3 With a particle size D50 of 40 μm, if added in excessive amounts when used alone, the microspheres will first float on the surface of the coating, causing hardening of the coating surface after prolonged storage. Secondly, the viscosity of the prepared coating will be too high, leading to production difficulties. Finally, the pigment volume concentration (PVC) of the coating formulation will exceed the critical pigment volume concentration (CPVC), resulting in a decline in the basic properties of the coating film. For example, when the addition amount of group 22 is 13.3%, the tensile adhesion of the coating film is only 3.0 MPa. In addition, since silica aerogel is a nanoporous material, when used alone, its specific surface area is as high as 600-800 m². 2 When the addition amount is high (e.g.), the coating exhibits greater thixotropy, making it difficult to disperse and potentially causing the PVC (polyvinyl chloride) in the coating formulation to exceed the CPVC (chemical PVC), leading to a decline in film performance. For example, when the addition amount of group 23 is 4.7%, the tensile adhesion of the coating film is only 3.2 MPa. Simultaneously, because the fillers such as finely precipitated barium sulfate, hollow glass microspheres, and silica aerogel added to the intermediate paint have low hiding power, adding a certain proportion of rutile titanium dioxide can improve both the hiding power and the reflectivity and radiative cooling effect of the coating film. Therefore, with a fixed amount of waterborne hydroxy acrylic dispersion, using a mixture of four different types of powders ensures both suitable storage and application viscosity of the coating, as well as the density and salt spray resistance of the coating film.

[0139] (3) Performance testing of two-component waterborne acrylic polyurethane topcoat The reflectance values ​​of coatings prepared using two-component waterborne acrylic polyurethane topcoats (groups 31, 32, and 34) were tested. The reflectance values ​​of coatings prepared with different types of titanium dioxide and the reflectance values ​​of coatings of different thicknesses (group 32) were also tested. The results are shown in […]. Figure 2 and 3 .

[0140] Depend on Figure 2 It is known that, for wavelengths of 200-1400 nm, the reflectance values ​​of coatings prepared from different types of titanium dioxide, in descending order, are: infrared reflective pigment W550 titanium dioxide, rutile titanium dioxide BLR-699, and infrared reflective pigment IR-1000 titanium dioxide. Considering the cost of raw materials for coatings, the topcoat pigment of this invention is infrared reflective pigment W550 titanium dioxide; the intermediate coat pigment is rutile titanium dioxide BLR-699.

[0141] Depend on Figure 3It can be seen that when the wavelength is 200-1400nm, the coating thickness of the white topcoat prepared in group 32 has a certain influence on the reflectivity. When the coating thickness is <80um, the reflectivity increases with the increase of the coating thickness, but when the coating thickness is >80um, the reflectivity remains basically unchanged. Therefore, in practical applications, the coating thickness of the topcoat is recommended to be around 80um.

[0142] (4) Testing of the basic properties and heat reflection properties of the coating system The coatings prepared using the coating system shown in Table 5 were tested according to HG / T4341-2012, and the results are shown in Tables 6-7. Figure 4 The coating system tested was as follows:

[0143] Supporting System 1: Two-component waterborne epoxy anti-corrosion primer (dry film thickness: 80±10um) + two-component waterborne acrylic polyurethane intermediate coat (dry film thickness: 300±20um) + two-component waterborne acrylic polyurethane topcoat (dry film thickness: 80±10um);

[0144] Supporting System 2: Two-component waterborne epoxy anti-corrosion primer (dry film thickness: 80±10um) + low-gloss two-component waterborne acrylic polyurethane topcoat (dry film thickness: 380±20um).

[0145] Table 5 Coating System

[0146]

[0147]

[0148] Table 6. Thermal reflectance properties of coating systems

[0149]

[0150] Table 7. Thermal reflectance properties of coating systems

[0151] Testing items index Supporting System 1 Supporting System 2 Solar reflectance ≥0.80 0.88 0.87 hemispherical emissivity ≥0.85 0.92 0.91 Near-infrared light reflectance ≥0.80 0.88 0.87 Atmospheric window (8-14µm) emissivity / 0.95 0.95 <![CDATA[Radiative cooling power / (W·m -2 )]]> ≥110 118 117

[0152] Depend on Figure 4 It can be seen that coating system 1 has a high reflectivity value, thus ensuring the effect of coating radiation cooling.

[0153] Table 5 shows that both coating systems 1 and 2 have good basic properties and heat reflection properties. However, the gloss of system 1 reaches 92, indicating that directly introducing hollow glass microspheres and silica aerogel into the topcoat will severely reduce the gloss performance of the coating. Nevertheless, since both coatings have good hydrophobic properties, stain resistance, and high decorative properties, system 2 is also a better choice when gloss is not a requirement.

[0154] In summary, compared with the prior art, the beneficial effects of the present invention also include:

[0155] (1) The present invention uses waterborne hydroxy acrylic dispersion and waterborne aliphatic isocyanate curing agent as film-forming substances, adds rutile titanium dioxide, silica aerogel and hollow glass microspheres, and supplements rheology modifiers, defoamers and substrate wetting agents to prepare a two-component waterborne acrylic polyurethane intermediate paint with good workability. The dry film thickness of a single coating can be greater than 100 μm. The composite use of multiple functional powders provides a guarantee for the excellent comprehensive performance of the coating film.

[0156] (2) The present invention uses waterborne hydroxy acrylic dispersion and waterborne aliphatic isocyanate curing agent as film-forming substances, adds infrared reflective rutile titanium dioxide, and supplements rheology modifiers, defoamers and substrate wetting agents to prepare a two-component waterborne acrylic polyurethane topcoat. The coating film has good gloss and comprehensive performance. The coating film of the matching system has high reflectivity and radiation cooling effect, and provides good corrosion resistance and decorative performance.

[0157] (3) Under the condition of ensuring the film thickness of the coating system, the environmentally friendly water-based coating can also have good anti-corrosion and radiation cooling effects when using the coating system of the present invention.

[0158] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A water-based radiation cooling coating for metal surfaces, characterized in that, include: Two-component waterborne epoxy anti-corrosion primer, two-component waterborne acrylic polyurethane intermediate coat, and two-component waterborne acrylic polyurethane topcoat; among which... The two-component waterborne epoxy anti-corrosion primer comprises: component A1 and component B1; based on the total of components A1 and B1 being 100%, component A1 comprises: 30%~40% waterborne epoxy emulsion, 1%~1.6% wetting and dispersing agent, 1%~5% organic bentonite slurry with a mass fraction of 2%~4%, 0.2%~0.5% defoamer, 0.4%~0.8% polyurethane rheology modifier, 5%~8% rutile titanium dioxide, 1%~3% metal oxide mixed-phase pigment, and mica powder. The composition includes: 2%~5%, finely precipitated barium sulfate 6%~10%, rust-preventive pigment 3%~6%, film-forming aid 0.3%~0.8%, substrate wetting agent 0.2%~0.4%, and deionized water 10%~20%; the B1 component includes: water-based epoxy curing agent 10%~15%, film-forming aid 0.3%~0.5%, anti-flash rust aid 0.1%~0.5%, and deionized water 10%~15%; the metal oxide mixed-phase pigment is at least one of zinc iron yellow, medium chrome yellow, titanium chrome brown, and titanium nickel yellow; The two-component waterborne acrylic polyurethane intermediate paint comprises: component A2 and component B2; based on the total of components A2 and B2 being 100%, component A2 comprises: 38%~45% waterborne hydroxyl acrylic dispersion, 0.8%~1.2% wetting and dispersing agent, 1%~5% organic bentonite slurry with a mass fraction of 2%~4%, 0.4%~0.8% polyurethane rheology modifier, 5%~8% film-forming aid, and 0.3%~ The composition includes: 0.7% rutile titanium dioxide, 6%~10% finely precipitated barium sulfate, 1%~3% silica aerogel, 6%~12% hollow glass microspheres, 0.1%~0.3% pH adjuster, 0.2%~0.4% substrate wetting agent, 0.1%~0.2% bactericide and preservative, and 5%~20% deionized water; Component B2 includes: 8%~15% aqueous isocyanate curing agent and 2%~4% propylene glycol diacetate. The two-component waterborne acrylic polyurethane topcoat consists of component A3 and component B3. Taking the total of components A3 and B3 as 100%, component A3 is composed of the following raw materials: 45%–55% waterborne hydroxyl acrylic dispersion, 0.8%–1.2% wetting and dispersing agent, 1%–5% organic bentonite slurry (2%–4% by mass), 0.4%–0.8% polyurethane rheology modifier, 5%–8% film-forming aid, 0.3%–0.7% defoamer, 20%–25% infrared reflective titanium dioxide, 0.1%–0.3% pH adjuster, 0.2%–0.4% substrate wetting agent, 0.2%–0.4% leveling agent, 0.1%–0.2% bactericide and preservative, and 1%–10% deionized water. Component B3 is composed of the following raw materials: 8%–15% waterborne isocyanate curing agent and 2%–4% propylene glycol diacetate.

2. The water-based radiation cooling coating for metal surfaces according to claim 1, characterized in that, The waterborne epoxy emulsion has a solid content of 50% to 60% by weight; the waterborne epoxy curing agent is at least one of modified aliphatic amine or modified polyamide, and the solid content of the waterborne epoxy curing agent is 35% to 45% by weight; the hydroxyl content of the waterborne hydroxyl acrylic dispersion is 3% to 4%, and the solid content of the waterborne hydroxyl acrylic dispersion is 40% to 60% by weight; the waterborne isocyanate curing agent is a waterborne aliphatic isocyanate curing agent, and the solid content of the waterborne isocyanate curing agent is >99% by weight.

3. The aqueous radiation cooling coating for metal surfaces according to claim 1, characterized in that, The anti-rust pigment is strontium zinc phosphosilicate; the rutile titanium dioxide is BLR-699; and the infrared reflective titanium dioxide is at least one of W550 and IR-1000.

4. The water-based radiation cooling coating for metal surfaces according to claim 1, characterized in that, The preparation method of the organic bentonite slurry with a mass fraction of 2% to 4% is as follows: add the organic bentonite rheology modifier to water, and after sufficient hydration, add a bactericide and preservative and mix evenly; wherein the bactericide and preservative accounts for 0.1% to 0.2% of the water mass.

5. The water-based radiation cooling coating for metal surfaces according to claim 1, characterized in that, The mass ratio of component A1 to component B1 is (3~4):1; the mass ratio of component A2 to component B2 is (7~9):1; and the mass ratio of component A3 to component B3 is (5~7):

1.

6. The water-based radiation cooling coating for metal surfaces according to claim 1, characterized in that, The film-forming aid is at least one of ethylene glycol butyl ether, dipropylene glycol monomethyl ether, dipropylene glycol butyl ether, and propylene glycol diacetate; the wetting and dispersing agent is at least one of DISPERBYK-190 and DISPERBYK-2012; the substrate wetting agent is TEGO Wet 270; the defoamer is at least one of TEGO® Airex902 W and BYK-028; the leveling agent is BYK-333; the anti-flash rust aid is ASCOTRAN® H10; the pH adjuster is an organic amine; and the bactericide and preservative is KATHON® LEX.

7. A method for preparing a water-based radiation-cooling coating for a metal surface as described in any one of claims 1 to 6, characterized in that, Includes the following steps: Preparation of a two-component waterborne epoxy anti-corrosion primer; Preparation of a two-component waterborne acrylic polyurethane intermediate varnish; Preparation of a two-component waterborne acrylic polyurethane topcoat; wherein, The preparation steps of the two-component waterborne epoxy anti-corrosion primer include: Under low-speed stirring, a portion of deionized water, wetting and dispersing agent, a portion of defoamer, organic bentonite slurry, and film-forming aid are dispersed evenly to obtain a first mixture. Under low-speed stirring, rutile titanium dioxide, metal oxide mixed-phase pigments, rust-preventing pigments, mica powder, and finely precipitated barium sulfate are added to the first mixture. After high-speed dispersion, the mixture is ground until the slurry fineness is ≤30μm to obtain a second mixture. Under low-speed stirring, an aqueous epoxy emulsion, substrate wetting agent, the remaining defoamer, polyurethane rheology modifier, and the remaining deionized water are added to the second mixture and dispersed evenly to obtain component A1. Deionized water, film-forming aid, and anti-flash rust aid were added to the water-based epoxy curing agent under low-speed stirring and dispersed evenly to obtain component B1; The preparation steps of the two-component waterborne acrylic polyurethane intermediate varnish include: Under low-speed stirring, the aqueous hydroxy acrylic dispersion, wetting and dispersing agent, part of the defoamer, organic bentonite slurry, film-forming aid, pH adjuster, and bactericide and preservative are dispersed evenly to obtain a first mixture. Under low-speed stirring, silica aerogel is added to the first mixture and dispersed evenly at high speed to obtain a second mixture. Under low-speed stirring, rutile titanium dioxide and finely precipitated barium sulfate are added to the second mixture and dispersed evenly at high speed to obtain a third mixture. Under low-speed stirring, the remaining defoamer, substrate wetting agent, polyurethane rheology modifier, and part of deionized water are added to the third mixture and dispersed evenly to obtain a fourth mixture. Under low-speed stirring, hollow glass microspheres and the remaining deionized water are added to the fourth mixture and dispersed evenly to obtain component A2. The film-forming aid was added to the aqueous isocyanate curing agent and dispersed evenly under low-speed stirring to obtain component B2. The preparation steps of the two-component waterborne acrylic polyurethane topcoat include: Under low-speed stirring, the aqueous hydroxy acrylic dispersion, wetting and dispersing agent, part of the defoamer, organic bentonite slurry, film-forming aid, pH adjuster, and bactericide and preservative are dispersed evenly to obtain a first mixture; infrared reflective titanium dioxide is added to the first mixture under low-speed stirring and dispersed evenly to obtain a second mixture; the remaining defoamer, substrate wetting agent, polyurethane rheology modifier, leveling agent, and deionized water are added to the second mixture under low-speed stirring and dispersed evenly to obtain component A3; The film-forming aid was added to the aqueous isocyanate curing agent and dispersed evenly under low-speed stirring to obtain component B3. The low-speed stirring speed is 500~1000 r / min, and the high-speed dispersion speed is 2000~2500 r / min.

8. A water-based radiation cooling coating for metal surfaces, characterized in that, The water-based radiation cooling coating on the metal surface is formed by curing the water-based radiation cooling coating for metal surfaces according to any one of claims 1 to 6; the water-based radiation cooling coating on the metal surface comprises: a two-component water-based epoxy anti-corrosion primer, a two-component water-based acrylic polyurethane intermediate coating, and a two-component water-based acrylic polyurethane topcoat; wherein... The two-component waterborne epoxy anti-corrosion primer is formed by curing the two-component waterborne epoxy anti-corrosion primer; The two-component waterborne acrylic polyurethane intermediate coating is formed by curing the two-component waterborne acrylic polyurethane intermediate paint; The two-component waterborne acrylic polyurethane topcoat is formed by curing the two-component waterborne acrylic polyurethane topcoat.

9. The aqueous radiation cooling coating for metal surfaces according to claim 8, characterized in that, The thickness of the two-component waterborne epoxy anti-corrosion primer is 70~90μm, the thickness of the two-component waterborne acrylic polyurethane intermediate coating is 280~320μm, and the thickness of the two-component waterborne acrylic polyurethane topcoat is 70~90μm.

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