Radiation refrigeration heat insulation coating and preparation method thereof

Abstract

The invention discloses a radiation refrigeration thermal insulation coating, which comprises a primer and a finish, the primer comprises deionized water, a pH regulator, a defoamer, hydroxypropyl methyl cellulose, a wetting agent, a dispersant, a waterborne polyurethane emulsion, aerogel, hollow glass beads, sepiolite and a film forming aid; the finish paint is prepared from deionized water, a PH regulator, a defoaming agent, hydroxypropyl methyl cellulose, a dispersing agent, silicon oxide, zirconium oxide, rutile type titanium dioxide, infrared reflection filler, a coalescing agent, a defoaming agent, far infrared ceramic powder, potassium silicate, silica sol, titanium sol, silane modified acrylic emulsion and conductive mica powder. The coating has the advantages of excellent sunlight reflectivity and infrared emissivity, low heat conductivity coefficient, excellent high temperature resistance, excellent flame retardance and excellent stain resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of coatings, and in particular relates to a radiative cooling and heat insulation coating. The present invention also relates to a preparation method of the coating. Background Art

[0002] For a long time, the sun has continuously transmitted a large amount of heat to the earth in various frequencies and wavelengths. Especially in the fields of building cooling, cold chain trucks for transportation, commodity refrigeration and preservation, petrochemical industry, power equipment, etc., it will have some negative impacts on people's production and life. As a new type of functional coating, the heat insulation coating can effectively reduce the accumulation of solar radiation heat on the surface of an object when applied to the surface of the object. The petrochemical industry is a large producer of energy, and at the same time a large energy consumer. A large number of pipelines and equipment need to be thermally insulated and cold-insulated. In addition, when applied to the surface of the building exterior wall, through its reflective heat insulation performance, it can effectively reduce the accumulation of heat generated by sunlight on the building exterior wall and reduce the heat transmitted into the room through the building wall, thereby reducing the energy consumption of the cooling equipment and improving the indoor environment. In order to reduce the surface temperature of an object under sunlight irradiation, prevent heat conduction, improve the working environment, and improve work safety, the reflective heat insulation coating, as a functional coating with outstanding energy-saving performance, is one of the most potential green materials. Summary of the Invention

[0003] The present invention provides a radiative cooling and heat insulation coating, which has excellent solar reflectivity and far-infrared emissivity. The present invention also combines a phase change energy storage heat insulation material with a low thermal conductivity material. The product has phase change energy storage heat insulation performance, excellent high-temperature flame retardancy and anti-fouling effect, and a long-term radiative cooling and heat insulation effect.

[0004] To achieve the above invention object, the present invention adopts the following technical solutions: A radiation cooling and heat insulation coating, the coating comprising a primer and a topcoat. The primer is composed of raw materials in the following weight parts: 65-75 parts of deionized water, 0.1-0.2 parts of a pH regulator, 0.2-0.5 parts of an antifoaming agent, 0.4-0.6 parts of hydroxypropyl methylcellulose, 1-1.5 parts of a wetting agent, 0.4-0.8 parts of a dispersant, 25-30 parts of an aqueous polyurethane emulsion, 7-15 parts of aerogel, 7-10 parts of hollow glass microspheres, 7-8 parts of sepiolite, 3-5 parts of a film-forming aid; the topcoat is composed of raw materials in the following weight parts: 25-35 parts of deionized water, 0.1-0.2 parts of a pH regulator, 0.1-0.3 parts of an antifoaming agent, 0.2-0.3 parts of hydroxypropyl methylcellulose, 0.4-0.8 parts of a dispersant, 2-5 parts of silicon oxide, 3-5 parts of zirconium oxide, 10-15 parts of rutile titanium dioxide, 10-16 parts of an infrared reflection filler, 2-3 parts of a film-forming aid, 0.1-0.2 parts of an antifoaming agent, 4-7 parts of far-infrared ceramic powder, 15-19 parts of potassium silicate, 8-12 parts of silica sol, 5-7 parts of titanium sol, 5-7 parts of a silane-modified acrylic emulsion, 3-4 parts of electrically conductive mica powder.

[0005] Further, the aerogel is a hydrophobic aerogel powder with a pore size of 20 nm.

[0006] Further, the rutile titanium dioxide is R-902 of DuPont, and the infrared reflection filler is a mixture of IR-1000 of Pan-China Chemical and W400 of Huntsman, and the mass ratio of IR-1000 to W400 is 1:1.

[0007] Further, the aqueous polyurethane emulsion is prepared from raw materials in the following weight parts according to the following preparation method: a. Preparation of polyurethane prepolymer: Add 55 parts of polyester polyol of Huada Chemical in a reactor under stirring, heat up to 70 °C, add 65 parts of isophorone diisocyanate, heat up to 80-85 °C under nitrogen protection, react until the measured -NCO content reaches the theoretical value, maintain the above rotation speed and temperature, add 30 parts of acetone, add 11 parts of 2,2-dimethylolpropionic acid and 0.1 part of dibutyltin dilaurate, react until the measured -NCO content reaches the theoretical value, add 5 parts of 1,4-butanediol to the reactor, and react until the measured -NCO content reaches the theoretical value to obtain a polyurethane prepolymer; b. Neutralization, emulsification and aqueous phase chain extension of the polyurethane prepolymer: Cool down to 35 °C, add 8 parts of triethanolamine, neutralize for 5 min, then add 180 parts of water, dilute and emulsify for 20 min, dissolve 2.5 parts of ethylenediamine in 30 parts of water, drop the ethylenediamine aqueous solution into the reaction system in 10-15 minutes, carry out an aqueous phase chain extension reaction for 2 h, and distill off methyl ethyl ketone under reduced pressure to obtain an aqueous polyurethane emulsion.

[0008] Furthermore, the primer contains 4 - 6 parts of phase change microcapsules, and the phase change microcapsules are prepared from the following raw materials in the following weight parts by the following preparation method: 1) Add 50 parts of paraffin wax with a melting point of 37°C, 16 parts of methyl methacrylate, 9 parts of methacrylic acid, 76 parts of deionized water, 1 part of anionic emulsifier, 1 part of non-ionic emulsifier, and 0.3 part of initiator azobisisobutyronitrile into an emulsification reactor. At a temperature 5°C higher than the melting point of paraffin wax, under a dispersion speed of 800 - 1200 r / min, emulsify for 30 minutes. Then reduce the stirring speed to 300 r / min, heat to 80 - 85°C and react for 3 hours. After that, add 1.5 parts of divinylbenzene and react for 3 h. Cool down to 65°C, and alternately add 0.05 part of oxidant tert-butyl hydroperoxide and 0.05 part of reductant FF6M in two times, with a time interval of 5 min. After the addition is completed, react at 65°C for 0.5 h; 2) Cool down to below 45°C, add 1 part of ammonia water and neutralize for 10 minutes. Filter the obtained phase change microcapsule emulsion, wash it with water 2 - 3 times, and then dry it to obtain the phase change microcapsules.

[0009] Furthermore, the modulus of the potassium silicate is 3.85 - 4.35.

[0010] Furthermore, the silica sol is a silane-modified silica sol.

[0011] Furthermore, the silane-modified silica sol is prepared from the following raw materials in the following weight parts by the following preparation method: S1: Add 12.5 parts of tetraethyl orthosilicate and 70 parts of ethanol into a reaction flask under stirring, heat up to 60°C, add 6.5 parts of deionized water, and dropwise add ammonia water to adjust the pH value to 8 - 9. Stir and react at 60°C for 2 h. Then add 50 parts of deionized water for dilution, heat to boiling, and reflux to remove ethanol and ammonia to obtain a silica sol prepolymer; S2: Cool down the silica sol prepolymer to 60°C, dropwise add 5.5 parts of tetraethyl orthosilicate, and add ammonia water to adjust the pH value of the reaction solution to 8 - 9, and react for 3 h; S3: Dropwise add 0.2 part of KH550 and 0.6 part of KH560 to modify the silica sol, react at 60°C for 1 h, and then concentrate by atmospheric distillation to obtain a modified silica sol with a solid content of 30%.

[0012] Furthermore, the titanium sol is anatase-type nano-titanium dioxide sol, and the silane-modified waterborne acrylic emulsion is KRN8101 of Jinrunna New Materials Co., Ltd., Heshan City.

[0013] For the preparation method of the above-mentioned radiation cooling and heat insulation coating, the primer is prepared by the following method: Step 1: Add deionized water, pH regulator, defoamer, hydroxypropyl methylcellulose, wetting agent, and dispersant into a reaction kettle. After dispersing evenly, add aerogel and stir until the aerogel is evenly dispersed to obtain an aerogel slurry. Step 2: Add aqueous polyurethane emulsion into a dispersion kettle. Under stirring, add hollow glass microspheres, sepiolite, film-forming aid, and aerogel slurry, and stir evenly to obtain the primer of the radiative cooling and heat insulation coating. The topcoat is prepared by the following method: Add deionized water, pH regulator, defoamer, hydroxypropyl methylcellulose, and dispersant into a reaction vessel, stir at 1800 r / min for 15 min, then add silica, zirconia, rutile titanium dioxide, infrared reflection filler, far-infrared ceramic powder, conductive mica powder, and stir at 1800 r / min for 30 min. Reduce the stirring speed to 600 r / min, add film-forming aid, silane-modified acrylic emulsion, defoamer, potassium silicate, silica sol, and titanium sol, and stir evenly to obtain the topcoat of the radiative cooling and heat insulation coating.

[0014] For the radiative cooling and heat insulation coating prepared by the present invention, the primer combines two types of phase change energy storage and heat insulation materials, namely aqueous polyurethane emulsion and phase change microcapsules, with low thermal conductivity, flame retardant, and fireproof materials such as aerogel, hollow glass microspheres, and sepiolite, and has a phase change energy storage and heat insulation effect. The topcoat has excellent solar light reflectivity and far-infrared radiation performance, can effectively reflect solar light, and emit its own heat in the form of electromagnetic waves to the outer space at absolute zero temperature to achieve the purpose of radiative cooling.

[0015] The topcoat of the present invention uses potassium silicate, silane-modified silica sol, titanium sol, and silane-modified aqueous acrylic emulsion as film-forming resins to form an organic-inorganic hybrid crosslinked structure, which has excellent water resistance, wear resistance, freeze-thaw resistance, and the overall coating has excellent high-temperature resistance, has A-level flame retardancy, heat insulation and noise reduction effects, and the topcoat combines photocatalytic self-cleaning property and antistatic adsorption property, has an antifouling, dustproof and self-cleaning effect, reduces the influence of dust accumulation on the coating surface on the reflection and radiation function of the coating, and has a long-term radiative cooling and heat insulation effect. Specific Embodiments

[0016] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0017] The aqueous polyurethane emulsion of the present invention is prepared from the following raw materials in the following weight parts by the following method: a. Preparation of polyurethane prepolymer: 55 parts of polyester polyol from Huada Chemistry were added to a reactor under stirring. The temperature was raised to 70°C, and 65 parts of isophorone diisocyanate were added. Under nitrogen protection, the temperature was raised to 80 - 85°C and reacted for 1.5 h. When the measured -NCO content reached the theoretical value, while maintaining the above rotation speed and temperature, 30 parts of acetone were added, followed by 11 parts of 2,2 - dimethylolpropionic acid and 0.1 part of dibutyltin dilaurate, and the reaction continued for 2 h until the measured -NCO content reached the theoretical value. Then 5 parts of 1,4 - butanediol were added to the reactor and reacted for 1 h until the measured -NCO content reached the theoretical value, thus obtaining the polyurethane prepolymer; b. Neutralization, emulsification and aqueous phase chain extension of polyurethane prepolymer: The temperature was lowered to 35°C, 8 parts of triethanolamine were added and neutralized for 5 min. Then 180 parts of water were added and diluted and emulsified for 20 min. 2.5 parts of ethylenediamine were dissolved in 30 parts of water, and the ethylenediamine aqueous solution was added dropwise to the reaction system within 10 - 15 minutes. The aqueous phase chain extension reaction was carried out for 2 h, and then methyl ethyl ketone was distilled off under reduced pressure to obtain the aqueous polyurethane emulsion.

[0018] The phase change microcapsules of the present invention are prepared from the following raw materials in parts by weight according to the following method: 1) 50 parts of paraffin with a melting point of 37°C, 16 parts of methyl methacrylate, 9 parts of methacrylic acid, 76 parts of deionized water, 1 part of anionic emulsifier, 1 part of non - ionic emulsifier and 0.3 part of initiator azobisisobutyronitrile were added to an emulsification reactor. At a temperature 5°C higher than the melting point of paraffin and under dispersion at a rotation speed of 800 - 1200 r / min, emulsification was carried out for 30 minutes. Then the stirring speed was reduced to 300 r / min, and the temperature was raised to 80 - 85°C and reacted for 3 h. Then 1.5 parts of divinylbenzene were added and reacted for 3 h. The temperature was lowered to 65°C, and 0.05 part of oxidant tert - butyl hydroperoxide and 0.05 part of reductant FF6M were alternately added in two portions with a time interval of 5 min. After the addition was completed, the reaction was carried out at 65°C for 0.5 h; 2) The temperature was lowered to below 45°C, 1 part of ammonia water was added and neutralized for 10 minutes. The obtained phase change microcapsule emulsion was filtered, washed with water 2 - 3 times, and then dried to obtain the phase change microcapsules. Examples

[0019] Examples 1 - 3 and Comparative Examples 1 - 4 respectively provided a radiation - cooling and heat - insulating paint primer, and the parts by weight of each raw material are shown in Table 1 below.

[0020] Table 1 Raw materials Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Deionized water 65 70 75 70 70 70 70 pH regulator 0.1 0.2 0.2 0.2 0.2 0.2 0.2 Defoamer 0.2 0.5 0.4 0.5 0.5 0.5 0.5 Hydroxypropyl methylcellulose 0.4 0.6 0.5 0.6 0.6 0.6 0.6 Wetting agent 1 1.5 1.2 1.5 1.5 1.5 1.5 Dispersant 0.4 0.8 0.6 0.8 0.8 0.8 0.8 Waterborne polyurethane emulsion 25 30 27 30 30 30 30（7026G） Aerogel 7 15 13 0 15 15 15 Phase change microcapsule 4 6 0 6 0 6 6 Hollow glass microsphere 7 10 8 25 16 18 10 Sepiolite 7 8 7.5 8 8 0 8 Film-forming aid 3 5 4 5 5 5 5 The above - mentioned aerogel is a hydrophobic aerogel powder with a pore size of 20 nm; the above - mentioned film - forming aid is alcohol ester 12; Comparative Example 4 uses acrylic emulsion 7026G from BASF.

[0021] Examples 1 to 3 and Comparative Examples 1 to 4, the preparation methods of the coatings provided specifically include the following steps: The primer is prepared by the following method: Step 1: Add deionized water, a pH regulator, an antifoaming agent, hydroxypropyl methylcellulose, a wetting agent, and a dispersant into a reaction kettle. After dispersing evenly, add aerogel and stir until the aerogel is evenly dispersed to obtain an aerogel slurry; Step 2: Add an aqueous polyurethane emulsion into a dispersion kettle. Under stirring, add hollow glass microspheres, sepiolite, a film-forming aid, the aerogel slurry, and phase change microcapsules and stir evenly to obtain the primer of the radiative cooling and heat insulation coating; For the primers of the radiative cooling and heat insulation coatings prepared in Examples 1 to 3 and Comparative Examples 1 to 4, relevant performance tests are carried out, and the test results are shown in Table 2 below.

[0022] Table 2 Item Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Surface drying time / min 36 35 33 30 34 45 35 Through drying time / h 4 4 4 4 4 4 4 Initial drying anti-cracking property (1mm) No abnormality No abnormality No abnormality No abnormality No abnormality Slight cracking No abnormality <![CDATA[Dry density (kg / m 3 )]]> 220 160 180 360 155 158 160 Thermal conductivity (W / (m·K)) 0.027 0.025 0.030 0.069 0.027 0.051 0.026 Heat insulation temperature difference of 1mm to 100℃ water (℃) 45 55 49 40 51 40 52 Bonding strength (MPa) 0.9 0.8 0.8 0.9 0.8 0.6 0.7 Alkali resistance (168h) No abnormality No abnormality No abnormality No abnormality No abnormality No abnormality No abnormality Water resistance (168h) No abnormality No abnormality No abnormality No abnormality No abnormality No abnormality No abnormality Coating temperature resistance change (10 cycles) No abnormality No abnormality No abnormality No abnormality No abnormality No abnormality No abnormality Test method for the heat insulation temperature difference (°C) of 1 mm against 100 °C water: Coat the primer of the radiative cooling and heat insulation coating with a dry film thickness of 1 mm on the surface of a stainless-steel cup. Pour 100 °C boiling water into the cup and measure the temperature T of the coating surface. The difference between 100 and T is the heat insulation temperature difference.

[0023] The weight parts of the respective raw materials of the topcoats corresponding to the primers of the radiative cooling and heat insulation coatings in Examples 1 to 3 and Comparative Examples 1 to 4 are shown in Table 3 below: Table 3 Raw materials Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Deionized water 25 35 30 30 30 30 30 pH regulator 0.1 0.2 0.1 0.1 0.1 0.1 0.1 Defoamer 0.1 0.3 0.2 0.2 0.2 0.2 0.2 Hydroxypropyl methylcellulose 0.2 0.3 0.2 0.2 0.2 0.2 0.2 Dispersant 0.4 0.8 0.6 0.6 0.6 0.6 0.6 Silica 2 5 4 4 4 4 4 Zirconia 5 3 4 4 4 4 7 Rutile titanium dioxide 10 15 12 4 12 12 12 IR-1000 5 6 8 12 0 8 8 W400 5 6 8 12 16 8 8 Film-forming aid 2 3 2.5 2.5 2.5 2.5 2.5 Defoamer 0.1 0.2 0.2 0.2 0.2 0.2 0.2 Far-infrared ceramic powder 4 7 6 6 6 6 6 Potassium silicate 15 19 17 17 17 23 17 Silica sol 8 12 10 10 10 10 10 Titanium sol 5 7 6 6 6 0 6 Silane-modified acrylic emulsion 5 7 6 6 6 6 6 Conductive mica powder 3 4 3 3 3 3 0 The above rutile titanium dioxide is R-902 of DuPont, and the modulus of the potassium silicate is 3.85 - 4.35. The titanium sol is anatase nano-titanium dioxide sol, and the silane-modified aqueous acrylic emulsion is KRN8101 of Jinrunna New Materials Co., Ltd., Heshan City.

[0024] The above silane-modified silica sol is prepared by the following method using the following weight parts of raw materials: S1: Add 12.5 parts of tetraethyl orthosilicate and 70 parts of ethanol into a reaction flask under stirring. Heat up to 60 °C, add 6.5 parts of deionized water, and dropwise add ammonia water to adjust the pH value to 8 - 9. Stir and react at 60 °C for 2 h. Then add 50 parts of deionized water for dilution, heat to boiling, and carry out reflux reaction to remove ethanol and ammonia gas to obtain a silica sol prepolymer; S2: Cool the silica sol prepolymer to 60 °C, dropwise add 5.5 parts of tetraethyl orthosilicate, and add ammonia water to adjust the pH value of the reaction solution to 8 - 9, and react for 3 h; S3: Dropwise add 0.2 parts of KH550 and 0.6 parts of KH560 to modify the silica sol, react at 60 °C for 1 h, and then concentrate by atmospheric distillation to obtain a modified silica sol with a solid content of 30%.

[0025] The topcoat described above is prepared by the following method: Add deionized water, pH regulator, defoamer, hydroxypropyl methylcellulose, and dispersant to a reaction vessel, stir at 1800 r / min for 15 min, then add silica, zirconia, rutile titanium dioxide, infrared reflection filler, far-infrared ceramic powder, conductive mica powder, stir at 1800 r / min for 30 min, reduce the stirring speed to 600 r / min, add film-forming aid, silane-modified acrylic emulsion, defoamer, potassium silicate, silica sol, and titanium sol, and stir evenly to obtain the topcoat of the radiation cooling and heat insulation coating.

[0026] Perform relevant performance tests on the topcoats of the radiation cooling and heat insulation coatings in Examples 1 to 3 and Comparative Examples 1 to 4. The specific test results are shown in Table 4 below.

[0027] Table 4 Item Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 State in container Uniform and no lumps after stirring Uniform and no lumps after stirring Uniform and no lumps after stirring Uniform and no lumps after stirring Uniform and no lumps after stirring Uniform and no lumps after stirring Uniform and no lumps after stirring <![CDATA[Acid resistance / (240 h) 10% H₂SO₄ 4 solution]]> No abnormality No abnormality No abnormality No abnormality No abnormality No abnormality No abnormality Alkali resistance / (240h) 10% NaOH solution No abnormality No abnormality No abnormality No abnormality No abnormality No abnormality No abnormality Water resistance / 30d No abnormality No abnormality No abnormality No abnormality No abnormality No abnormality No abnormality Combustion performance Grade A Grade A Grade A Grade A Grade A Grade A Grade A Coating temperature resistance change (10 cycles) No abnormality No abnormality No abnormality No abnormality No abnormality No abnormality No abnormality Resistivity (Ω) <![CDATA[10 8 > <![CDATA[10 7 > <![CDATA[10 8 > <![CDATA[10 8 > <![CDATA[10 8 > <![CDATA[> 10 12 > <![CDATA[> 10 12 > Mildew resistance Grade 0 Grade 0 Grade 0 Grade 0 Grade 0 Grade 0 Grade 0 Damp heat resistance / d The coating has no cracking, no blistering, and no wrinkling after 7d The coating has no cracking, no blistering, and no wrinkling after 7d The coating has no cracking, no blistering, and no wrinkling after 7d The coating has no cracking, has blistering, and has wrinkling after 7d The coating has no cracking, has blistering, and has wrinkling after 7d The coating has no cracking, has blistering, and has wrinkling after 7d The coating has no cracking, no blistering, and no wrinkling after 7d Freeze-thaw resistance / times After 15 cycles, the coating has no blistering, no wrinkling, and no peeling After 15 cycles, the coating has no blistering, no wrinkling, and no peeling After 15 cycles, the coating has no blistering, no wrinkling, and no peeling After 15 cycles, the coating has no blistering, no wrinkling, and no peeling After 15 cycles, the coating has no blistering, no wrinkling, and no peeling After 15 cycles, the coating has no blistering, no wrinkling, and no peeling After 15 cycles, the coating has no blistering, no wrinkling, and no peeling Stain resistance 6% 5% 6% 6% 6% 11% 12% Reflectivity % 97 98 97 97 96 97 97 Reflectivity % after dry powder (fly ash) pollution 96 97 96 96 95 90 91 Solar reflectance 89 90 88 80 88 89 89 Near-infrared reflectance 89 88 90 91 83 89 89 Hemispherical emissivity 87 89 88 85 85 87 88 Artificial aging resistance No blistering, no cracking, and no peeling after 1000h No blistering, no cracking, and no peeling after 1000h No bubbling, cracking or peeling after 1000h No bubbling, cracking or peeling after 1000h No bubbling, cracking or peeling after 1000h No bubbling, cracking or peeling after 1000h No bubbling, cracking or peeling after 1000h Measurement of reflectivity after contamination with dry powder (fly ash): Sprinkle fly ash dry powder evenly on the surface of the dry sample coating, stand up the sample and shake off the fly ash on the coating surface, and measure the reflectivity of the coating surface with a reflectivity measuring instrument.

[0028] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, or improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A radiant cooling and thermal insulation coating, characterized in that: The coating comprises a primer and a topcoat, wherein the primer is composed of the following raw materials in parts by weight: 65-75 parts of deionized water, 0.1-0.2 parts of a pH regulator, 0.2-0.5 parts of a defoamer, 0.4-0.6 parts of hydroxypropyl methylcellulose, 1-1.5 parts of a wetting agent, 0.4-0.8 parts of a dispersant, 25-30 parts of an aqueous polyurethane emulsion, 7-15 parts of an aerogel, 7-10 parts of hollow glass microspheres, 7-8 parts of sepiolite, and 3-5 parts of a film-forming aid; the topcoat is composed of the following raw materials in parts by weight: 25 -35 parts, PH regulator 0.1-0.2 parts, defoamer 0.1-0.3 parts, hydroxypropyl methylcellulose 0.2-0.3 parts, dispersant 0.4-0.8 parts, silicon oxide 2-5 parts, zirconium oxide 3-5 parts, rutile titanium dioxide 10-15 parts, infrared reflective filler 10-16 parts, film-forming aid 2-3 parts, defoamer 0.1-0.2 parts, far-infrared ceramic powder 4-7 parts, potassium silicate 15-19 parts, silica sol 8-12 parts, titanium sol 5-7 parts, silane-modified acrylic emulsion 5-7 parts, conductive mica powder 3-4 parts.

2. The radiant cooling and thermal insulation coating according to claim 1, characterized in that: The aerogel is a hydrophobic aerogel powder with a pore size of 20 nm.

3. The radiant cooling and thermal insulation coating according to claim 1, characterized in that: The rutile titanium dioxide is DuPont's R-902, and the infrared reflective filler is a mixture of Pan-China Chemical's IR-1000 and Pan-Energy's W400, and the mass ratio of IR-1000 to W400 is 1:

1.

4. The radiant cooling and thermal insulation coating according to claim 1, characterized in that: The aqueous polyurethane emulsion is prepared by using the following raw materials in parts by weight according to the following preparation method: a. Preparation of polyurethane prepolymer: 55 parts of polyester polyol of Huada Chemical were added to the reactor under stirring, the temperature was raised to 70°C, 65 parts of isophorone diisocyanate were added, the temperature was raised to 80-85°C under nitrogen protection, and the -NCO content measured reached the theoretical value. The above speed and temperature were maintained, 30 parts of acetone were added, 11 parts of 2,2-dihydroxymethylpropionic acid and 0.1 parts of dibutyltin dilaurate were added, and the -NCO content measured reached the theoretical value. 5 parts of 1,4-butanediol were added to the reactor, and the -NCO content measured reached the theoretical value to obtain a polyurethane prepolymer; b. Neutralization, emulsification and water-phase chain extension of polyurethane prepolymer: cool to 35°C, add 8 parts of triethanolamine, neutralize for 5 minutes, then add 180 parts of water, dilute and emulsify for 20 minutes, dissolve 2.5 parts of ethylenediamine in 30 parts of water, add the ethylenediamine aqueous solution dropwise to the reaction system over 10-15 minutes, carry out chain extension reaction in the water phase for 2 hours, distill off butanone under reduced pressure to obtain a waterborne polyurethane emulsion.

5. The radiant cooling and thermal insulation coating according to claim 1, characterized in that: The primer contains 4-6 parts of phase change microcapsules, and the phase change microcapsules are prepared by using the following raw materials in parts by weight according to the following preparation method: 1) Add 50 parts of paraffin wax with a melting point of 37°C, 16 parts of methyl methacrylate, 9 parts of methacrylic acid, 76 parts of deionized water, 1 part of anionic emulsifier, 1 part of nonionic emulsifier and 0.3 parts of initiator azobisisobutyronitrile into an emulsification reactor, emulsify for 30 minutes at a temperature 5°C higher than the melting point of paraffin wax and a speed of 800-1200 r / min, reduce the stirring speed to 300 r / min, heat to 80-85°C and react for 3 hours, then add 1.5 parts of divinylbenzene and react for 3 hours, cool to 65°C, add 0.05 parts of oxidant tert-butyl hydroperoxide and 0.05 parts of reducing agent FF6M alternately twice, with a time interval of 5 minutes, and react at 65°C for 0.5 hours after the addition is completed; 2) Cooling to below 45° C., adding 1 part of ammonia water for neutralization for 10 minutes, filtering the obtained phase change microcapsule emulsion, washing with water for 2-3 times, and drying to obtain phase change microcapsules.

6. The radiant cooling and thermal insulation coating according to claim 1, characterized in that: The modulus of the potassium silicate is 3.85-4.

35.

7. The radiant cooling and thermal insulation coating according to claim 1, characterized in that: The silica sol is silane-modified silica sol.

8. The radiant cooling and thermal insulation coating according to claim 7, characterized in that: The silane-modified silica sol is prepared by the following method, and the raw materials are in parts by weight: S1: Add 12.5 parts of ethyl orthosilicate and 70 parts of ethanol in a reaction bottle under stirring, heat to 60°C, add 6.5 parts of deionized water, add ammonia water dropwise to adjust the pH value to 8-9, stir and react at 60°C for 2h, then add 50 parts of deionized water to dilute, heat to boiling, reflux reaction, remove ethanol and ammonia, and obtain a silica sol prepolymer; S2: Cool the silica sol prepolymer to 60°C, add 5.5 parts of ethyl orthosilicate dropwise, and add ammonia water to adjust the pH value of the reaction solution to 8-9, and react for 3 hours; S3: 0.2 parts of KH550 and 0.6 parts of KH560 were added dropwise to modify the silica sol, reacted at 60°C for 1 hour, and then concentrated by atmospheric distillation to obtain a modified silica sol with a solid content of 30%.

9. The radiant cooling and thermal insulation coating according to claim 1, characterized in that: The titanium sol is anatase nano titanium dioxide sol; the silane-modified water-based acrylic emulsion is KRN8101 produced by Heshan Jinrunna New Materials Co., Ltd.

10. A method for preparing a radiation cooling and thermal insulation coating according to any one of claims 1 to 9, characterized in that: The primer is prepared by the following method: Step 1: Add deionized water, pH regulator, defoamer, hydroxypropyl methylcellulose, wetting agent and dispersant into a reactor, add aerogel after uniform dispersion, and stir until the aerogel is uniformly dispersed to obtain aerogel slurry; Step 2: Add water-based polyurethane emulsion into a dispersion kettle, add hollow glass microspheres, sepiolite, film-forming aid, and aerogel slurry under stirring, and stir evenly to obtain a primer for radiant cooling and thermal insulation coating; The topcoat is prepared by the following method: Deionized water, pH regulator, defoamer, hydroxypropyl methylcellulose and dispersant are added to a reaction container and stirred at 1800 r / min for 15 min. Then silicon oxide, zirconium oxide, rutile titanium dioxide, infrared reflective filler, far-infrared ceramic powder and conductive mica powder are added and stirred at 1800 r / min for 30 min. The stirring speed is reduced to 600 r / min, and film-forming aid, silane-modified acrylic emulsion, defoamer, potassium silicate, silica sol and titanium sol are added and stirred evenly to obtain a topcoat of radiant refrigeration and thermal insulation coating.