Temperature-responsive color-changing microcapsules, methods of making the same, coatings, and architectural coatings

Abstract

The application discloses a temperature response color-changing microcapsule, a preparation method thereof, paint and a building coating, and belongs to the field of building radiant refrigeration materials. The preparation method of the temperature response color-changing microcapsule comprises the following steps: mixing calcium-based carbonized powder, a regulation aid and water, and performing a carbonization reaction with carbon dioxide to obtain precursor wet material A; mixing the precursor wet material A, an alkaline aid and water, and performing a reaction to obtain a first filter cake product and a second filtrate product; mixing the first filter cake product, a complexing agent and water, and performing a reaction, and then performing washing and drying to obtain precursor powder B; mixing the precursor powder B and an organic pigment to obtain precursor C; mixing the precursor C and the second filtrate product, and performing a reaction, and then performing solid-liquid separation to obtain solid precursor powder D; and coating a polymer on the surface of the precursor powder D to obtain the temperature response color-changing microcapsule. The method can solve the technical problems of poor ultraviolet durability and poor thermal cycle of the temperature response color-changing microcapsule in the prior art.

Description

Technical Field

[0001] This invention relates to the field of building radiant cooling materials, and in particular to a temperature-responsive color-changing microcapsule and its preparation method, as well as coatings and building coatings. Background Technology

[0002] Radiative cooling technology effectively mitigates the urban heat island effect, requiring no mechanical structures or electrical power during operation, offering advantages in energy conservation and emission reduction, and promising broad application prospects. However, currently developed radiative cooling materials struggle to cope with my country's complex and challenging geographical environment, varying solar radiation, and climate, limiting their widespread adoption. Buildings in different regions have varying performance requirements in different seasons. While high reflectivity and emissivity radiative cooling materials can provide higher cooling capacity, they are insufficient for meeting the insulation and heating needs of cold regions or winter conditions. Furthermore, highly reflective radiative cooling materials are generally white, and large-scale application can cause glare interference to the eyes of living organisms.

[0003] To address the aforementioned issues, introducing temperature-responsive color-changing microcapsules to prepare dynamic coatings has become an effective approach. Dynamic coatings can actively adjust between dark and light states based on ambient temperature. At low temperatures, they exhibit a dark state, demonstrating high absorption of solar photon energy to meet solar heating requirements; at high temperatures, they exhibit a light state, exhibiting low absorption and high reflection of solar photon energy to avoid additional heat input and meet radiative cooling needs.

[0004] However, temperature-responsive color-changing capsules have poor UV durability, causing dynamic coatings to easily lose their temperature-responsive function or color after a period of solar radiation. Therefore, there is an urgent need to develop a new type of temperature-responsive color-changing microcapsule to promote the large-scale application of radiative cooling technology on building surfaces and further reduce energy consumption and carbon emissions in building temperature management. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned technical deficiencies and propose a temperature-responsive color-changing microcapsule and its preparation method, coatings and building coatings, to solve the technical problems of poor UV durability and poor thermal cycling of temperature-responsive color-changing capsules in the prior art.

[0006] To achieve the above-mentioned technical objectives, a first aspect of the present invention provides a method for preparing temperature-responsive color-changing microcapsules, comprising the following steps: mixing calcium-based carbonized powder, a regulating agent, and water, and reacting the mixture with carbon dioxide to obtain a precursor wet material A; mixing the precursor wet material A, an alkaline agent, and water, and filtering the mixture to obtain a first filter cake product and a second filtrate product; mixing the first filter cake product, a complexing agent, and water, and washing and drying the mixture to obtain a precursor powder B; mixing the precursor powder B with an organic pigment to obtain a precursor C, wherein the organic pigment includes a color-changing agent, a color-developing agent, and a solvent; mixing the precursor C with the second filtrate product, and separating the solid to obtain a solid precursor powder D, wherein the mass ratio of the precursor C to the second filtrate product is 1:(10-100), and the pH value of the reaction between the precursor C and the second filtrate product is 4-7.5; and coating the surface of the precursor powder D with a polymer to obtain temperature-responsive color-changing microcapsules.

[0007] In some embodiments, the calcium-based carbonized powder includes one or more of dicalcium silicate, tricalcium silicate, monocalcium silicate, and disaccharide silicate; and / or, the average particle size of the calcium-based carbonized powder is 0.3 micrometers to 10 micrometers; and / or, the regulating agent includes one or more of magnesium chloride, magnesium nitrate, magnesium sulfate, and magnesium citrate; and / or, the mass ratio of the calcium-based carbonized powder, the regulating agent, and water is 1:(0.0001-0.5):(1-65); and / or, the carbonization reaction temperature is 20℃-80℃, and the time is 1h-24h.

[0008] In some embodiments, the alkaline additive includes one or more of sodium hydroxide, sodium carbonate, sodium silicate, and ammonia water; and / or, the pH value of the reaction of the precursor wet material A, the alkaline additive, and water is 7.1-13.5; and / or, the temperature of the reaction of the precursor wet material A, the alkaline additive, and water is 20℃-50℃, and the time is 1h-24h.

[0009] In some embodiments, the complexing agent includes one or more of disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, tricarboxylic acid, citric acid, and tartaric acid; and / or, the mass ratio of the first filter cake product, the complexing agent, and water is 1:(0.02-15):(50-500); and / or, the temperature for mixing and reacting the first filter cake product, the complexing agent, and water is 20°C-50°C, and the time is 0.5h-24h.

[0010] In some embodiments, the precursor powder B and the organic pigment are mixed under vacuum conditions; and / or, the organic pigment accounts for 2%-50% of the mass of the precursor powder B; and / or, the mass ratio of the color-changing agent, the color-developing agent, and the solvent is (1-10):(3-20):(70-96); and / or, the color-changing agent includes one of fluorane materials, spiropyrans, spiroxazines, or triarylmethanes; and / or, the color-developing agent includes one or more of phthalic acid, oxalic acid, p-aminophenol, naphthol, bisphenol A, and salicylic acid; and / or, the solvent is a fatty alcohol, including one or more of dodecyl alcohol, tetradecyl alcohol, hexadecyl alcohol, octadecyl alcohol, isooctadecyl alcohol, ethylene glycol, propylene glycol, glycerol, methyl dodecanoate, methyl hexadecanoate, methyl octadecanoate, methyl oleate, and methyl linoleate.

[0011] In some embodiments, the reaction time between the precursor C and the second filtrate product is 60 min to 600 min.

[0012] In some embodiments, the polymer includes one or more of phenolic resin, urea-formaldehyde resin, melamine-formaldehyde resin, polyurethane, and polyurea; and / or, the step of coating the precursor powder D with the polymer includes: dispersing the precursor powder D in water to form a suspension, adding the polymer and mixing, and vacuum drying.

[0013] In a second aspect, the present invention provides a temperature-responsive color-changing microcapsule, which is prepared using the method described in the first aspect of the present invention.

[0014] In a third aspect of the invention, the invention provides a coating comprising temperature-responsive color-changing microcapsules prepared using the method described in the first aspect of the invention.

[0015] In a fourth aspect, the present invention provides an architectural coating comprising the coatings described in the third aspect of the present invention.

[0016] Compared with the prior art, the beneficial effects of the present invention include: In the preparation method of temperature-responsive color-changing microcapsules, the first step involves optimizing the reaction between calcium-based carbonized powder and carbon dioxide by regulating additives. This generates particles with aragonite-type calcium carbonate and silica gel as the main products in the wet precursor A, forming aragonite-type calcium carbonate coating silica gel and unreacted calcium-based carbonized powder. The regulating additives significantly inhibit the formation of calcite-type calcium carbonate and promote the precipitation of needle-like aragonite crystals on the surface of the calcium-based carbonized powder. The advantage of aragonite-type calcium carbonate crystals lies in their loose and porous surface microstructure, which facilitates surface modification. Simultaneously, nano-aragonite-type calcium carbonate crystals possess a high band gap and high refractive index, enabling them to efficiently scatter incident ultraviolet light back without affecting sunlight in the visible and infrared bands. This weakens the irradiation process of ultraviolet light on the capsules and organic pigments, thus enhancing the capsule's lifespan and color performance.

[0017] To highlight the advantages of the three-dimensional loose and porous structure, the second step uses an alkaline solution formed by an alkaline additive to dissolve the silica gel, preserving the stable structure of the aragonite-type calcium carbonate crystal framework, while retaining abundant pores inside the material.

[0018] The complexing agent in the third step has a strong chelating ability for calcium ions. On the one hand, the complexing agent reacts with the unreacted calcium-based carbonized powder to treat the residual calcium ions; on the other hand, the complexing agent produces a micro-etching effect on the surface of aragonite-type calcium carbonate crystals, forming an ideal microstructure and promoting the grafting of functional groups on the surface of aragonite-type calcium carbonate crystals, improving interfacial compatibility, which is helpful for the dense coating of subsequent polymer materials and the preparation of precursor powder D.

[0019] In the fourth step, the organic pigments exhibit vibrant colors, temperature sensitivity, and reversible color changes. Specifically, when the ambient temperature is above the melting point of the fatty alcohol material, the liquid fatty alcohol dissolves the color developer, which blocks the reaction between the color developer and the color changer. The lactone ring of the color changer closes, and the temperature-responsive color-changing microcapsules as a whole exhibit low absorption and high scattering within the solar spectrum, resulting in a white appearance. When the ambient temperature is below the melting point of the fatty alcohol material, the fatty alcohol solidifies, and the precipitated color developer reacts with the color changer, promoting the opening of the lactone ring. This results in high absorption and low scattering within the solar spectrum, resulting in a darker appearance. By combining different color developers and color changers within the capsules, different colors can be produced, and by using different fatty alcohol materials, different temperature-responsive effects can be achieved.

[0020] Further, using the dissolved silica gel solution and the second filtrate product as raw materials, a preliminary coating is applied to the surface of the precursor C filled with organic pigment. The silica gel is then re-coated onto the surface of the aragonite crystal to form a silica gel layer. The silica gel layer has the effect of inhibiting pigment leakage and promoting the bonding performance between aragonite-type calcium carbonate and polymer materials. A polymer layer is further coated on the outside of the silica gel layer to enhance the protective effect of the silica gel layer and is suitable for various coating matrices.

[0021] In summary, this invention, through a designed depolymerization and condensation process, reshapes the spatial structure of precursors primarily composed of aragonite-type calcium carbonate and silica gel, forming a stable porous structure with an internal aragonite-type calcium carbonate framework, an outer layer of silica gel, and polymer coating, and is filled with temperature-responsive organic pigments. The optical band gap of aragonite-type calcium carbonate and silica gel is higher than the energy of solar photons in the ultraviolet region. The scattering process limits the incidence of ultraviolet light and its irradiation of the temperature-responsive color-changing microcapsules, which, in combination, helps protect the organic pigments inside the microcapsules and the color expression of the capsules. Furthermore, this invention proposes temperature-responsive color-changing microcapsules that exhibit good compatibility with coatings of different matrices, transforming static coatings with only radiative cooling functions into dynamic coatings that combine radiative cooling and solar heating functions, thus meeting the temperature management needs of buildings in both hot and cold weather conditions. Attached Figure Description

[0022] Figure 1 This is a schematic flowchart of the preparation method of temperature-responsive color-changing microcapsules proposed in the embodiments of the present invention; Figure 2 This is the XRD pattern of the calcium-based carbonized powder prepared in Example 1 of this invention; Figure 3 These are DSC images of the temperature-responsive color-changing microcapsules prepared in Examples 1 and 2 of this invention; Figure 4 This is a SEM image of the temperature-responsive color-changing microcapsules prepared in Example 1 of the present invention. Detailed Implementation

[0023] 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.

[0024] In a first aspect, the present invention provides a method for preparing temperature-responsive color-changing microcapsules; please refer to [link to relevant documentation]. Figure 1 The method includes the following steps: S1. Mix calcium-based carbonized powder, regulating agent, and water, and react with carbon dioxide to obtain precursor wet material A.

[0025] In this step, by regulating the additives to optimize the reaction between calcium-based carbonized powder and carbon dioxide, particles with aragonite-type calcium carbonate and silica gel as the main products can be generated in the precursor wet material A. This results in aragonite-type calcium carbonate coating silica gel and unreacted calcium-based carbonized powder. The regulating additives significantly inhibit the formation of calcite-type calcium carbonate and promote the precipitation of needle-like aragonite crystals on the surface of the calcium-based carbonized powder. The advantage of aragonite-type calcium carbonate crystals lies in their loose and porous surface microstructure, which facilitates surface modification. Simultaneously, nano-aragonite-type calcium carbonate crystals possess a high band gap and a high refractive index, enabling them to efficiently scatter incident ultraviolet light back without affecting sunlight in the visible and infrared bands. This weakens the irradiation process of ultraviolet light on the capsules and organic pigments, thus enhancing the capsule's lifespan and color performance.

[0026] In some embodiments, the calcium-based carbonized powder includes one or more of dicalcium silicate (such as β-C2S, γ-C2S), tricalcium silicate, monocalcium silicate, and disaccharide. The above-mentioned calcium-based carbonized powder readily reacts with carbon dioxide to form aragonite-type calcium carbonate and silica gel.

[0027] It is understandable that the aforementioned calcium-based carbonized powder can be purchased or prepared by oneself.

[0028] In some embodiments, the average particle size of the calcium-based carbonized powder is 0.3 micrometers to 10 micrometers. Examples include 0.3 micrometers, 0.5 micrometers, 1 micrometer, 3 micrometers, 5 micrometers, 7 micrometers, 9 micrometers, 10 micrometers, or any combination of two of the above values, thereby facilitating the obtaining of a precursor wet material A with a suitable average particle size.

[0029] In some embodiments, the regulating agent includes one or more of magnesium chloride, magnesium nitrate, magnesium sulfate, and magnesium citrate. These regulating agents can optimize the reaction between calcium-based carbide powder and carbon dioxide, significantly inhibit the formation of calcite-type calcium carbonate, and promote the precipitation of needle-like aragonite crystals on the surface of the calcium-based carbide powder.

[0030] In some embodiments, the mass ratio of the calcium-based carbonized powder, the regulating agent, and water is 1:(0.0001-0.5):(1-65). As an example, the mass ratio can be 1:0.0001:1, 1:0.0001:30, 1:0.0001:65, 1:0.25:1, 1:0.25:30, 1:0.25:65, 1:0.5:1, 1:0.5:30, 1:0.5:65, or any range of two of the above values. Thus, the regulating agent is sufficient to optimize the reaction between the calcium-based carbonized powder and carbon dioxide, significantly inhibit the formation of calcite-type calcium carbonate, and promote the precipitation of needle-like aragonite crystals on the surface of the calcium-based carbonized powder.

[0031] In some embodiments, the purity (volume fraction or mole fraction) of the carbon dioxide reacting with the calcium-based carbonation powder, regulating agent, and water mixture is 50%-99%. For example, the purity of the carbon dioxide can be 50%, 60%, 70%, 80%, 90%, 99%, or any combination of two of the above values. This allows for sufficient carbonization of the calcium-based carbonation powder to form aragonite-type calcium carbonate and inhibits the formation of calcite-type calcium carbonate.

[0032] In some embodiments, the carbonization reaction temperature is 20°C-80°C, and the time is 1h-24h. As an example, the carbonization reaction temperature can be 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, or any combination of two of these values; the carbonization reaction time can be 1h, 3h, 5h, 8h, 10h, 12h, 15h, 18h, 20h, 24h, or any combination of two of these values. This facilitates at least partial carbonization of the calcium-based carbonized powder, promoting the formation of aragonite-type calcium carbonate.

[0033] S2. The precursor wet material A, alkaline additive and water are mixed and reacted, and then filtered to obtain the first filter cake product and the second filtrate product.

[0034] In this step, an alkaline solution formed by an alkaline additive is used to dissolve the silica gel, preserving the stable structure of the aragonite-type calcium carbonate crystal framework, while the material retains abundant pores inside.

[0035] In some embodiments, the alkaline additive includes one or more of sodium hydroxide, sodium carbonate, sodium silicate, and ammonia. The alkaline additive is alkaline and capable of dissolving at least a portion of the silica gel in the wet precursor A, resulting in abundant porosity in the wet precursor A.

[0036] In some embodiments, the pH value of the mixture of precursor wet material A, alkaline additive, and water is 7.1-13.5. For example, it can be 7.1, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, or any two of the above values. This allows at least a portion of the silica gel in precursor wet material A to dissolve, resulting in abundant pores in precursor wet material A without damaging its structure.

[0037] In some embodiments, the temperature for mixing and reacting the precursor wet material A, the alkaline additive, and water is 20°C-50°C, and the time is 1h-24h. As an example, the temperature for the mixing reaction can be 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, or any combination of two of these values, and the reaction time can be 1h, 3h, 5h, 8h, 10h, 12h, 15h, 18h, 20h, 24h, or any combination of two of these values. This further facilitates the dissolution of at least a portion of the silica gel in the precursor wet material A, resulting in abundant pores in the precursor wet material A.

[0038] S3. The first filter cake product, complexing agent and water are mixed and reacted, washed and dried to obtain precursor powder B.

[0039] In this step, the complexing agent has a strong chelating ability for calcium ions. On the one hand, the complexing agent reacts with the unreacted calcium-based carbonized powder to treat the residual calcium ions; on the other hand, the complexing agent produces a micro-etching effect on the surface of aragonite-type calcium carbonate crystals, forming an ideal microstructure and promoting the grafting of functional groups on the surface of aragonite-type calcium carbonate crystals, improving interfacial compatibility, which is helpful for the dense coating of subsequent polymer materials and the preparation of precursor powder D.

[0040] In some embodiments, the complexing agent includes one or more of disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, tricarboxylic acid, citric acid, and tartaric acid. These substances, acting as complexing agents, facilitate the removal of residual calcium ions from the first filter cake product and further improve the interfacial compatibility of precursor powder B, contributing to the dense coating of subsequent polymer materials and the preparation of precursor powder D.

[0041] In some embodiments, the mass ratio of the first filter cake product, the complexing agent, and water is 1:(0.02-15):(50-500). As an example, the mass ratio of the three components can be 1:0.02:50, 1:0.02:300, 1:0.02:500, 1:7.5:50, 1:7.5:300, 1:7.5:500, 1:15:50, 1:15:300, 1:15:500, or any range of two of the above values. This further facilitates the removal of residual calcium ions from the first filter cake product, forming a precursor powder B with a better morphology.

[0042] In some embodiments, the temperature for mixing the first filter cake product, the complexing agent, and water is 20°C-50°C, and the time is 0.5h-24h. As an example, the mixing reaction temperature can be 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, or any combination of two of these values. The mixing reaction time can be 0.5h, 1h, 3h, 5h, 8h, 10h, 12h, 15h, 18h, 20h, 24h, or any combination of two of these values. This further facilitates the removal of residual calcium ions from the first filter cake product, forming a precursor powder B with a better morphology.

[0043] In some embodiments, drying can be performed using vacuum drying, which can improve the structural stability of the obtained product.

[0044] S4. The precursor powder B and the organic pigment are mixed to obtain precursor C, wherein the organic pigment includes a color changer, a color developer, and a solvent.

[0045] In this step, the organic pigments exhibit vibrant colors, temperature sensitivity, and reversible color change. Specifically, when the ambient temperature is above the melting point of the fatty alcohol material, the liquid fatty alcohol dissolves the color developer, which blocks the reaction between the color developer and the color changer. The lactone ring of the color changer closes, and the temperature-responsive color-changing microcapsules as a whole exhibit low absorption in the solar spectrum, resulting in a white appearance. When the ambient temperature is below the melting point of the fatty alcohol material, the fatty alcohol solidifies, and the precipitated color developer reacts with the color changer, promoting the opening of the lactone ring and exhibiting high absorption in the solar spectrum, resulting in a dark appearance. By combining different color developers and color changers within the capsules, different colors can be produced.

[0046] In some embodiments, the precursor powder B and the organic pigment are mixed under vacuum conditions. Vacuum mixing, i.e., vacuum loading, allows for the low-cost and efficient incorporation of organic pigments into the precursor powder B, resulting in a stable filling content and improving color performance.

[0047] In some embodiments, the organic pigment accounts for 2%-50% of the mass of the precursor powder B. As an example, it can be 2%, 5%, 10%, 20%, 30%, 40%, 50%, or any combination of two of the above values. Thus, a stable amount of organic pigment can be formed in the precursor C, so that the temperature-sensitive color-changing microcapsules exhibit different colors at different temperatures.

[0048] In some embodiments, the mass ratio of the color-changing agent, the color-developing agent, and the solvent is (1-10):(3-20):(70-96). As an example, the mass ratio of the three can be 1:3:70, 1:10:83, 1:10:96, 1:20:83, 5:3:70, 5:20:83, 5:20:96, 5:10:70, 5:10:96, or any range of two of the above values. This allows for the formation of a stable organic pigment filling amount in the precursor C, enabling the temperature-sensitive color-changing microcapsules to exhibit different colors at different temperatures.

[0049] In some embodiments, the color-changing agent includes one of fluorane materials, spiropyrans, spiroxazines, or triarylmethanes; and / or, the color-developing agent includes one or more of phthalic acid, oxalic acid, p-aminophenol, naphthol, bisphenol A, and salicylic acid; as an example, fluorane materials may include one or more of 6'-(diethylamino)-1',2'-benzofluorane, dichlorodihydrofluorescein, melanin 1, and 2'-(dibenzylamino)-6'-(diethylamino)fluorane. Thus, the color-changing agent and color-developing agent of the above materials can exhibit different colors, and different materials of color-changing agents can be selected according to requirements.

[0050] In some embodiments, the solvent is a fatty alcohol, including one or more of dodecyl alcohol, tetradecyl alcohol, hexadecyl alcohol, octadecyl alcohol, isooctadecyl alcohol, ethylene glycol, propylene glycol, glycerol, methyl dodecanoate, methyl hexadecanoate, methyl octadecanoate, methyl oleate, and methyl linoleate. As an example, the fatty alcohol material may include one or more of methyl octadecanoate and methyl octadecanoate. This makes the organic pigment temperature-sensitive.

[0051] S5. The precursor C is mixed and reacted with the second filtrate product, and the solid is separated to obtain the precursor powder D. The mass ratio of the precursor C to the second filtrate product is 1:(10-100), and the pH value of the mixture of the precursor C and the second filtrate product is 4-7.5.

[0052] In this step, the dissolved silica gel solution and the second filtrate product are used as raw materials to initially coat the surface of the precursor C filled with organic pigment. The silica gel is then re-coated on the surface of the aragonite crystal to form a silica gel layer. The silica gel layer has the effect of inhibiting pigment leakage and promoting the bonding performance between aragonite-type calcium carbonate / polymer materials.

[0053] As an example, the mass ratio of precursor C to the second filtrate product can be 1:10, 1:30, 1:50, 1:70, 1:90, 1:100 or any two of the above ranges. This allows a silica gel coating layer of moderate thickness to be formed on the surface of precursor C, further suppressing pigment leakage and promoting the bonding performance between aragonite-type calcium carbonate and polymer materials.

[0054] As an example, the pH value of the reaction between precursor C and the second filtrate product can be 4, 5, 6, 7, 7.5 or any two of the above values. This allows a stable silica gel coating layer to be formed on the surface of precursor C, further suppressing pigment leakage and promoting the bonding performance between aragonite-type calcium carbonate and polymer materials.

[0055] In some embodiments, the reaction time between the precursor C and the second filtrate product is 60 min to 600 min. As an example, the reaction time can be 60 min, 100 min, 200 min, 300 min, 400 min, 500 min, 600 min, or any combination of two of these values. This further facilitates the formation of a moderately thick and stable silica gel coating layer on the surface of the precursor C, further suppressing pigment leakage and promoting the bonding performance between aragonite-type calcium carbonate and polymer materials.

[0056] S6. Coat the surface of the precursor powder D with a polymer to obtain temperature-responsive color-changing microcapsules.

[0057] In this step, the polymer is further coated on the outside of the silicone gel layer to enhance the protective effect of the silicone gel layer and make it suitable for a variety of coating matrices.

[0058] In some embodiments, the polymer includes one or more of phenolic resin, urea-formaldehyde resin, melamine-formaldehyde resin, polyurethane, and polyurea. The polymers of the above materials exhibit high stability, which can further improve the stability of the material, and they are compatible with other materials used in coatings.

[0059] In some embodiments, the step of coating the precursor powder D with a polymer includes: dispersing the precursor powder D in water to form a suspension, adding the polymer and mixing, and then vacuum drying. This results in a more uniform and stable polymer coating layer.

[0060] In summary, this invention, through a designed depolymerization and condensation process, reshapes the spatial structure of the precursors, primarily aragonite-type calcium carbonate and silica gel, forming a stable porous structure with an internal aragonite-type calcium carbonate framework, an outer layer of silica gel, and polymer coating, and is filled with temperature-responsive organic pigments. The optical band gap of aragonite-type calcium carbonate and silica gel is higher than the energy of solar photons in the ultraviolet region, and the scattering process limits the incidence of ultraviolet light and its irradiation of the capsules. Simultaneously, the photocatalytic effect of the aragonite crystalline phase is weaker than that of titanium dioxide. All these factors combined are beneficial for protecting the organic pigments inside the temperature-responsive color-changing microcapsules and the color expression of the capsules. Furthermore, the temperature-responsive color-changing microcapsules proposed in this invention exhibit good compatibility with coatings of different matrices, transforming static coatings with only radiative cooling functions into dynamic coatings that combine radiative cooling and solar heating functions, meeting the temperature management needs of buildings in both hot and cold weather conditions.

[0061] In a second aspect, the present invention provides a temperature-responsive color-changing microcapsule, which is prepared using the method described in the first aspect of the present invention.

[0062] The temperature-responsive color-changing microcapsules proposed in the second aspect of this invention possess all the beneficial effects of the preparation method in the first aspect, which will not be elaborated here.

[0063] In a third aspect of the invention, the invention provides a coating comprising temperature-responsive color-changing microcapsules prepared using the method described in the first aspect of the invention.

[0064] As an example, the coating may also contain other components such as nano high-reflectivity fillers, such as calcium carbonate, alumina, boron nitride, barium sulfate, calcium sulfate, barium titanate, zinc oxide or titanium oxide, solvents such as cyclohexane, and other components such as polymethylpentene particles (PMP).

[0065] The coating proposed in the third aspect of this invention possesses all the beneficial effects of the preparation method in the first aspect, which will not be elaborated here.

[0066] In a fourth aspect, the present invention provides an architectural coating comprising the coatings described in the third aspect of the present invention.

[0067] The aforementioned building coatings can form a dynamic coating on building surfaces that has both radiative cooling and solar heating properties.

[0068] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0069] Example 1 Calcium-based carbide powder was prepared by calcining analytically pure raw materials. The powder was weighed and mixed uniformly according to a molar ratio of calcium hydroxide to silicon dioxide of 2:1, and then calcined at 1400℃ for approximately 3 hours. After natural cooling, the calcium-based carbide powder was prepared. The XRD pattern of the calcium-based carbide powder is shown below. Figure 2 As shown, XRD quantitative analysis revealed that the mass fraction of γ-C2S in the calcium-based carbonized powder reached over 97%. Following the procedure, the calcium-based carbonized powder, magnesium chloride (a regulating agent), and water were weighed and stirred in a mass ratio of 1:0.01:5 to form a uniform slurry. 90% pure carbon dioxide was introduced, the water bath temperature was controlled at 30 degrees Celsius, and the reaction time was controlled at 14 hours. After washing, the precursor wet material A was obtained.

[0070] A combination of sodium hydroxide and sodium carbonate was used as an alkaline additive, with the mass ratio of sodium hydroxide to sodium carbonate controlled at 1:1.6. The mixture was mixed with wet precursor A and reacted. The pH of the solution was controlled at 12, the reaction temperature at 38 degrees Celsius, and the reaction time at 6 hours. The first filter cake product and the second filtrate product were obtained by filtration.

[0071] Using disodium ethylenediaminetetraacetate as a complexing agent, a slurry with a mass ratio of the first filter cake product, complexing agent and water of 1:5:100 was prepared. The reaction temperature was controlled at 30℃ and the reaction time was 6h. After washing, the precursor powder B was obtained by vacuum drying.

[0072] A ternary organic pigment system was prepared by mixing fluorane materials (2.5 parts by mass of 6'-(diethylamino)-1',2'-benzofluorane and 0.5 parts by mass of dichlorodihydrofluorescein), a color developer (10 parts by mass of bisphenol A), and fatty alcohols (13 parts by mass of methyl octadecyl carbonate and 74 parts by mass of methyl octadecyl acid). The precursor powder B and the liquid organic pigment were simultaneously placed in a vacuum reactor, and then the vacuum was maintained to further mix the precursor powder B and the organic pigment. After waiting for 30 minutes, the vacuum was released and the mixture was taken out to obtain the precursor C.

[0073] The mass ratio of precursor C to the second filtrate product was controlled at 1:50, the pH value of the reaction was controlled at 5.5, the reaction time was controlled at 120 min, and the filtered cake was further vacuum dried to obtain precursor powder D.

[0074] Precursor D was added to an aqueous solution containing sodium dodecyl sulfate as an emulsifier, and a homogeneous suspension was formed by high-speed stirring to induce shear fractionation. The solution temperature was controlled at 60°C and the pH at 7. Polymer raw materials consisting of aminotriazine cyclic resin and styrene-maleic anhydride random copolymer were added dropwise to the suspension. After reacting for 12 hours, a melamine-formaldehyde resin coating layer was formed by surface crosslinking and curing. After washing and vacuum drying, temperature-responsive color-changing microcapsules were obtained.

[0075] DSC images of the temperature-responsive color-changing microcapsules prepared in Examples 1 and 2 are shown below. Figure 3 As shown, the color change point of the capsules was confirmed to be around 31 degrees Celsius through comprehensive thermal analysis (DSC). Below the color change point, the capsules appear red; above the color change point, the capsules appear light-colored.

[0076] SEM image of the temperature-responsive color-changing microcapsules prepared in Example 1 is shown below. Figure 4 As shown, the capsule is relatively intact.

[0077] Example 2 The difference between this embodiment and Example 1 is that the color-changing agent in the organic pigment formulation is changed to 2.5 parts by weight of melanin 1 (7-Anilino-3-diethylamino-6-methyl fluoran) and 0.5 parts by weight of 2'-(dibenzylamino)-6'-(diethylamino)fluorane, while the content of the color developer and fatty alcohols remains unchanged.

[0078] Example 3 The difference between this embodiment and Example 1 lies in the different calcium-based carbonized powder. Analytical raw materials were weighed according to a molar ratio of calcium hydroxide to silicon dioxide of 2.3:1, and 0.005 parts of boric acid were introduced as a crystal stabilizer. The raw materials were mixed evenly and subjected to the same calcination process to prepare the calcium-based carbonized powder. XRD quantitative analysis revealed a composition of approximately 84% β-C2S and 15% tricalcium silicate.

[0079] Example 4 The difference between this embodiment and Example 1 lies in the different alkaline auxiliaries and complexing agents. In this embodiment, the alkaline auxiliaries consist of sodium carbonate and ammonia in a 1:1 molar ratio, with a solution pH of 10.6, a reaction temperature of 40 degrees Celsius, and a reaction time of 12 hours. The complexing agents in this embodiment consist of ethylenediaminetetraacetic acid and citric acid in a 1:1 molar ratio, with the reaction temperature controlled at 40 degrees Celsius and the reaction time at 12 hours.

[0080] Example 5 In this embodiment, the temperature-responsive color-changing microcapsules prepared in Examples 1 to 4 are introduced into the coating matrix to prepare a coating. The coating is then applied to the glass surface to form a thin film of uniform thickness (300 μm) using a simple scraping method, and its reflectance spectra in both colored and colorless states are tested.

[0081] The following formula was used: polymethylpentene particles (PMP, as the matrix carrier capsule): cyclohexane: nano-calcium carbonate filler: temperature-responsive color-changing microcapsules were weighed in a mass ratio of 14:200:7:0.5. First, a homogeneous PMP / cyclohexane solution was prepared by completely dissolving the PMP in cyclohexane. Then, the calcium carbonate filler and the temperature-responsive color-changing microcapsules prepared in the above example were added sequentially and stirred until homogeneous to obtain the desired coating. A smooth film was then scraped onto the glass surface using a doctor blade and further dried in a vacuum drying oven to obtain the film required for the experiment. The films obtained in Examples 1, 2, 3, and 4 correspond to Examples 5-1, 5-2, 5-3, and 5-4, respectively.

[0082] Example 6 The difference between this embodiment and Example 1 lies in the organic pigment formulation. In this embodiment, the fatty alcohol consists of 47 parts methyl octadecyl carbonate and 40 parts methyl octadecyl acid, and the mixing method with the color developer and color changer remains unchanged. The process of vacuum loading into the precursor powder also remains unchanged.

[0083] Example 7 The difference between this embodiment and Example 1 is that the regulating agent used is different. In this embodiment, magnesium sulfate and magnesium citrate are mixed in a molar ratio of 1:1 and introduced into the preparation process.

[0084] Comparative Example 1 The difference between this comparative example and Example 1 is that no regulating agent is used, and the reaction temperature is controlled at 25 degrees Celsius and the reaction time is controlled at 6 hours during the regulating step S1.

[0085] Comparative Example 2 The difference between this comparative example and Example 1 is that, in the subsequent preparation of precursor powder C, no color-changing agent fluorane or color-developing agent is introduced; only the same mass of fatty alcohol material is filled.

[0086] Comparative Example 3 The difference between this comparative example and Example 1 is that the prepared precursor powder B was further soaked in dilute hydrochloric acid (pH 12) for 24 hours to completely eliminate the aragonite-type calcium carbonate framework formed on the surface of the calcium-based carbonized powder. The subsequent preparation process remained unchanged.

[0087] Comparative Example 4 The difference between this comparative example and Example 1 is that the precursor powder C prepared does not undergo further processing using the second filtrate product, and the precursor powder is directly coated with polymer material.

[0088] Comparative Example 5 The difference between this embodiment and Example 1 lies in the different coating reaction conditions of the second filtrate product. In this comparative example, in step S5, the mass ratio of precursor C to the second filtrate product was changed to 1:50, the reaction pH was controlled to be 8.2, and the reaction time was 400 min.

[0089] Comparative Example 6 The difference between this embodiment and Example 1 lies in the different coating reaction conditions of the second filtrate product. In this comparative example, in step S5, the mass ratio of precursor C to the second filtrate product is changed to 1:200, the reaction pH is controlled to be 8.2, and the reaction time is 400 min.

[0090] Experimental Test The prepared temperature-responsive color-changing microcapsules were tested. After 100 temperature cycles within the range of 10°C to 50°C, the color performance before and after the phase transition temperature was evaluated using a colorimeter. An optical microscope was used to assess the integrity of the capsules after 100 temperature cycles. UV durability testing was conducted using laboratory UV lamps to accelerate aging and assess the UV resistance of the temperature-responsive color-changing properties. A larger color difference value ΔE indicates more severe UV damage. Based on CIE standards, ΔE < 1.0 means the color change is almost imperceptible to the human eye. ΔE < 3.0 indicates a slight color difference, but meets the minimum requirements for architectural coatings; ΔE > 5.0 indicates a severe color difference.

[0091] The test results are shown in Table 1.

[0092] Table 1

[0093] The test results in Table 1 show that the temperature-responsive color-changing microcapsules prepared by the method disclosed in the embodiments of this invention can meet the standards in both ultraviolet durability tests and thermal cycling tests. This verifies that the method of using calcium carbonate as the main spatial framework and silica gel depolymerization-repolymerization can effectively improve the problems of poor ultraviolet durability and poor thermal cycling of temperature-responsive color-changing capsules, and has promotional value.

[0094] In Example 3, due to the modification of the calcium-based carbonization raw materials, the hydration activity of β-C2S and tricalcium silicate is stronger during the preparation process, resulting in the formation of more hydration product layers on the surface. This inhibits the carbonization reaction and reduces the content of aragonite-type calcium carbonate, and the microstructure is not conducive to protecting the organic pigments. In Example 6, the different fatty alcohol material formulations result in a temperature transition point of approximately 10°C for the temperature-responsive color-changing capsules, making them unsuitable for buildings in temperate climates, but suitable for urban buildings in northern or high-latitude regions.

[0095] In Comparative Example 1, the lack of regulating agents and the lower reaction temperature were detrimental to the formation of aragonite-type calcium carbonate crystals, but beneficial to the formation of calcite crystals. Calcite crystals are large and have weak cross-bonding properties on the surface of calcium-based carbonized powder, hindering the formation of a porous structure and making it difficult to provide more storage space for organic pigments. Their large size also causes them to scatter more visible light, resulting in a pinkish tint to the temperature-responsive color-changing capsules, losing their red appearance. In Comparative Example 2, the lack of chromogenic and color-changing agents caused the temperature-responsive color-changing capsules to lack a basis for color change. Only comprehensive thermal analysis could confirm the thermal signal, but it was difficult to distinguish the color change, resulting in no significant change in the spectral properties of the temperature-responsive color-changing capsules. In Comparative Example 3, the lack of aragonite crystals to protect the organic pigments made the pigments more susceptible to UV degradation, resulting in significant color differences. Comparative Examples 4-6 further illustrate the importance of the silica gel coating layer. The lack of a coating layer or the formation of uneven silica gel aggregates in a highly alkaline environment can lead to pigment leakage during polymer coating treatment, which is detrimental to the structural integrity of the temperature-responsive color-changing capsules.

[0096] Spectral testing The reflectance spectra before and after the color change were measured using an ultraviolet-visible-infrared spectrometer, and the test results are shown in Table 2.

[0097] Table 2

[0098] Polymethylpentene, a polymer, is highly transparent in the solar radiation band and absorbs almost no solar photons. Table 2 shows that incorporating the temperature-responsive color-changing capsules of this invention into the coating exhibits excellent temperature response capabilities. The differences in reflectivity among different embodiments can be addressed by selecting the capsule type based on variations in ambient temperature. Different spectral properties can be obtained by simply adjusting the preparation process of the temperature-responsive color-changing capsules. Low reflectivity is chosen for optimal heating performance, while high reflectivity is chosen for optimal radiative cooling performance.

[0099] 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 method for preparing temperature-responsive color-changing microcapsules, characterized in that, Includes the following steps: Calcium-based carbonized powder, regulator, and water are mixed and then carbonized with carbon dioxide to obtain precursor wet material A. The precursor wet material A, alkaline additive and water are mixed and reacted, and then filtered to obtain the first filter cake product and the second filtrate product; The first filter cake product, complexing agent and water are mixed and reacted, washed and dried to obtain precursor powder B; The precursor powder B is mixed with an organic pigment to obtain precursor C, wherein the organic pigment includes a color changer, a color developer, and a solvent. The precursor C is mixed and reacted with the second filtrate product, and the solid is separated to obtain the precursor powder D. The mass ratio of the precursor C to the second filtrate product is 1:(10-100), and the pH value of the mixture of the precursor C and the second filtrate product is 4-7.

5. A polymer is coated onto the surface of the precursor powder D to obtain temperature-responsive color-changing microcapsules.

2. The method for preparing temperature-responsive color-changing microcapsules according to claim 1, characterized in that, The calcium-based carbonized powder includes one or more of dicalcium silicate, tricalcium silicate, monocalcium silicate, and tricalcium disilicate; and / or, The average particle size of the calcium-based carbonized powder is 0.3 micrometers to 10 micrometers; and / or, The regulating agent includes one or more of magnesium chloride, magnesium nitrate, magnesium sulfate, and magnesium citrate; and / or, The mass ratio of the calcium-based carbonized powder, the regulating agent, and water is 1:(0.0001-0.5):(1-65); and / or, The carbonization reaction is carried out at a temperature of 20℃-80℃ for 1h-24h.

3. The method for preparing temperature-responsive color-changing microcapsules according to claim 1, characterized in that, The alkaline additive includes one or more of sodium hydroxide, sodium carbonate, sodium silicate, and ammonia water; and / or, The pH value of the reaction between the wet precursor A, the alkaline additive, and water is 7.1-13.5; and / or, The reaction temperature of the wet precursor A, alkaline additive and water is 20℃-50℃, and the reaction time is 1h-24h.

4. The method for preparing temperature-responsive color-changing microcapsules according to claim 1, characterized in that, The complexing agent comprises one or more of the following: disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, tricarboxylic acid, citric acid, and tartaric acid; and / or, The mass ratio of the first filter cake product, the complexing agent, and water is 1:(0.02-15):(50-500); and / or, The temperature for mixing and reacting the first filter cake product, complexing agent, and water is 20℃-50℃, and the time is 0.5h-24h.

5. The method for preparing temperature-responsive color-changing microcapsules according to claim 1, characterized in that, The precursor powder B and the organic pigment are mixed under vacuum conditions; and / or, The organic pigment accounts for 2%-50% of the mass of the precursor powder B; and / or, The mass ratio of the color-changing agent, the color-developing agent, and the solvent is (1-10):(3-20):(70-96); and / or, The color-changing agent includes one of fluorane materials, spiropyrans, spiroxazines, or triarylmethanes; and / or, The colorimetric agent includes one or more of phthalic acid, oxalic acid, p-aminophenol, naphthol, bisphenol A, and salicylic acid; and / or, The solvent is a fatty alcohol, including one or more of the following: dodecyl alcohol, tetradecyl alcohol, hexadecyl alcohol, octadecyl alcohol, isooctadecyl alcohol, ethylene glycol, propylene glycol, glycerol, methyl dodecanoate, methyl hexadecanoate, methyl octadecanoate, methyl oleate, and methyl linoleate.

6. The method for preparing temperature-responsive color-changing microcapsules according to claim 1, characterized in that, The reaction time between the precursor C and the second filtrate product is 60 min to 600 min.

7. The method for preparing temperature-responsive color-changing microcapsules according to claim 1, characterized in that, The polymer includes one or more of phenolic resin, urea-formaldehyde resin, melamine-formaldehyde resin, polyurethane, and polyurea; and / or, The step of coating the precursor powder D with polymer includes: dispersing the precursor powder D in water to form a suspension, adding the polymer and mixing, and vacuum drying.

8. A temperature-responsive color-changing microcapsule, characterized in that, The temperature-responsive color-changing microcapsules are prepared using the method described in any one of claims 1-7.

9. A coating, characterized in that, The coating comprises temperature-responsive color-changing microcapsules, which are prepared by the method described in any one of claims 1-7.

10. A building coating, characterized in that, The building coating includes the coating as described in claim 9.

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