Attapulgite-coated titanium dioxide, reflective thermal insulation coating and preparation method thereof

Abstract

The invention relates to attapulgite-coated titanium dioxide, a reflective thermal insulation coating and a preparation method thereof, and the preparation method of the attapulgite-coated titanium dioxide comprises the following steps: S1, treating attapulgite with hydrochloric acid to remove impurities to obtain purified attapulgite, and carrying out surface modification treatment with a titanate coupling agent to obtain modified attapulgite; s2, titanium dioxide inorganic coating slurry is taken, the modified attapulgite and deionized water are mixed to prepare suspension liquid, the suspension liquid is mixed with the titanium dioxide inorganic coating slurry, and mixed slurry is obtained; s3, the mixed slurry is filtered, washed, subjected to flash evaporation and subjected to steam pulverizing, and the attapulgite-coated titanium dioxide is obtained. The use ratio of the titanium dioxide can be reduced, and the reflection performance, dispersity and stability of the titanium dioxide can be improved.

Description

Technical Field

[0001] This invention relates to an attapulgite-coated titanium dioxide, a reflective heat-insulating coating, and its preparation method. This invention relates to the field of outdoor water-based coating technology. Background Technology

[0002] Against the backdrop of the global push for "dual carbon" goals and the escalating energy crisis, reflective thermal insulation technology, as a core means of reducing energy consumption in buildings, transportation, and industrial equipment, is experiencing explosive growth in demand. This technology utilizes the high reflectivity of materials to solar radiation (especially visible and near-infrared light with wavelengths of 0.3-2.5μm) to reduce heat absorption and simultaneously reduce infrared radiation dissipation from the material itself into the environment, thereby achieving temperature regulation of the protected object. It is widely used in building exteriors / roofs, container bodies, new energy vehicle battery packs, industrial storage tanks and pipelines, and other scenarios. Therefore, developing reflective thermal insulation technology that combines high solar radiation reflectivity (visible light ≥90%, near-infrared ≥85%), excellent weather resistance (reflectivity decay ≤5% after more than 1000 hours of artificial aging), adaptability to multiple scenarios (rigid / flexible, high and low temperatures, lightweight), and controllable cost is crucial for overcoming existing technological bottlenecks and driving the upgrading of the reflective thermal insulation industry, possessing urgent technological demand and enormous market value.

[0003] Titanium dioxide is an important raw material in existing reflective heat-insulating coatings, possessing excellent light reflection properties that significantly impact the quality of these coatings. However, the high cost of titanium dioxide raw materials affects the overall cost of the coating. Furthermore, the stability of the titanium dioxide in the coating also affects its service life. In outdoor applications, prolonged exposure to sunlight and rain can lead to the oxidation and hydrolysis of titanium dioxide particles, resulting in structural damage and a decline in reflective heat-insulating performance. Summary of the Invention

[0004] The purpose of this invention is to provide an environmentally friendly exterior wall reflective heat insulation coating that is cost-controllable and adaptable to multiple application scenarios. It can meet the requirements of infrared reflection cooling while taking into account the stability and economy of the coating / product.

[0005] A method for preparing attapulgite-coated titanium dioxide includes the following steps: S1 attapulgite is treated with hydrochloric acid to remove impurities, resulting in purified attapulgite. Then, it is surface modified with a titanate coupling agent to obtain modified attapulgite. S2 Take titanium dioxide inorganic coating slurry, mix modified attapulgite clay with deionized water to make a suspension, and mix it with titanium dioxide inorganic coating slurry to obtain mixed slurry; The S3 mixture slurry is filtered, washed, flash-evaporated, and steam-dried to obtain attapulgite-coated titanium dioxide.

[0006] Preferably, in step S2, the amount of modified attapulgite added is 10-15% of the mass of titanium dioxide in the inorganic coating slurry. Adding too much modified attapulgite will significantly reduce the reflectivity of the coated titanium dioxide; adding too little will have little effect.

[0007] Preferably, in step S2, the solid content of the suspension is 50 wt%, and 5 wt‰ sodium polycarboxylate is added to the suspension.

[0008] Preferably, in step S1, the surface modification treatment involves adding purified attapulgite to an alcohol solvent, dispersing it to form a suspension, and then adding a titanate coupling agent at 3%-5% of the mass of the purified attapulgite. The mixture is stirred at a constant temperature of 60-70℃ for 1.5-2 hours, where the alkoxy groups of the titanate react with the hydroxyl groups on the surface of the attapulgite to undergo a de-alcoholization condensation reaction, introducing hydrophobic long chains. The solvent is removed by vacuum distillation (temperature 65-75℃, vacuum degree (-0.08)~(-0.09MPa)), and the mixture is dried at 120℃ for 2 hours, then pulverized to obtain titanate-modified attapulgite. The residual titanate groups on the surface of the modified attapulgite further react with the hydroxyl groups on the surface of titanium dioxide to form a chemical bond, preventing physical detachment.

[0009] Preferably, the alcohol solvent is anhydrous ethanol or isopropanol.

[0010] This invention claims protection for attapulgite-coated titanium dioxide prepared by the above-described preparation method.

[0011] After titanium dioxide is coated with titanate-modified attapulgite, its infrared reflectance performance can be improved, while its dispersibility, stability and weather resistance can be enhanced.

[0012] The introduction of hydrophobic long-chain groups (such as isostearyl groups) on the surface of titanate-modified attapulgite is a reactive group that matches the hydroxyl groups on the surface of titanium dioxide. The titanate groups of the modified attapulgite can undergo a "de-alcoholization condensation reaction" with the hydroxyl groups on the surface of titanium dioxide again to form a stable chemical bond, thus preventing the two from agglomerating in coatings and other systems.

[0013] Titanium dioxide, after being inorganically coated (with silica, alumina, and zinc oxide), retains over 80% of its reflectivity in the near-infrared band (700-2500nm). Modified attapulgite further enhances this property through "structural complementarity." Firstly, it enhances scattering through porous structure. The natural fibrous porous structure of attapulgite, even after being coated with titanate esters, retains some pores, resulting in a "multiple scattering-reflection" effect on incident infrared light, reducing the probability of infrared light absorption by the substrate. Secondly, it modulates the refractive index. The refractive index difference between attapulgite (refractive index approximately 1.5-1.6) and titanium dioxide (rutile type, refractive index approximately 2.7) creates a "micro-interface refractive index gradient" after their composite formation, enhancing the reflection efficiency in the infrared band and increasing the near-infrared reflectivity of the composite system by 5%-15%, reaching over 90%.

[0014] In addition, the titanium dioxide coated with attapulgite can also produce the following effects: First, it improves dispersibility. The hydrophobic long chains on the surface of the modified attapulgite can be better compatible with organic resins (such as acrylic resin and fluorocarbon resin) in the coating, while avoiding the agglomeration between titanium dioxide particles, thus improving the uniformity and hiding power of the coating. Second, it enhances weather resistance. The fibrous structure of attapulgite can "physically block" the erosion of titanium dioxide by ultraviolet rays and moisture, and strengthen the reflection and scattering of ultraviolet rays. The incident ultraviolet rays will be "multiple scattering" at the multiple interfaces of "titanium dioxide-attapulgite-resin", which is more efficient in scattering ultraviolet rays, reduces the penetration of ultraviolet rays into the substrate, and extends the coating life.

[0015] Based on the attapulgite-coated titanium dioxide prepared according to this invention, this invention further provides a reflective heat-insulating coating, comprising the following components by weight: 10-20 parts deionized water, 0.2-0.4 parts hydrophobically modified cellulose, 2-5 parts additives, 6-12 parts modified silica aerogel, 6-10 parts graded hollow microspheres, 5-8 parts nano-crack-resistant additives, 15-25 parts attapulgite-coated titanium dioxide, 3-8 parts modified precipitated barium sulfate, 25-45 parts pure acrylic emulsion, and 0.3-0.5 parts thickener.

[0016] Preferably, the additives include wetting agents, dispersants, defoamers, film-forming agents, antifreeze agents, and bactericides and preservatives.

[0017] The method for preparing the reflective heat-insulating coating of the present invention includes the following steps: S11: Add deionized water to the stirring device, and while stirring, add hydrophobically modified cellulose sequentially. After the hydrophobically modified cellulose dissolves, add the wetting agent, dispersant, defoamer, and film-forming agent. Stir evenly, then switch to high-speed stirring. S12 is added sequentially with nano-crack-resistant additive, modified silica aerogel, graded hollow microspheres, attapulgite-coated titanium dioxide, modified precipitated barium sulfate, and pH adjuster. After high-speed stirring and uniform dispersion, the stirring speed is adjusted to low speed until the dispersion is ≤50μm. Pure acrylic emulsion, defoamer, antifreeze, bactericide and preservative, and thickener are added and stirred evenly to obtain the product.

[0018] The beneficial effects of this invention are twofold: First, it allows for the partial replacement of titanium dioxide with attapulgite, reducing the proportion of titanium dioxide used and thus lowering raw material costs. Second, coating titanium dioxide with attapulgite improves its reflectivity, dispersibility, and stability. The attapulgite-coated titanium dioxide of this invention, when used in coatings, can enhance the reflective and heat-insulating properties of the coatings. Attached Figure Description

[0019] Figure 1 A comparison image of titanium dioxide and purified attapulgite.

[0020] Figure 2 Comparison of the reflectivity of titanium dioxide coated with attapulgite clay of different coating amounts. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0022] In order to improve the weather resistance, dispersibility and hiding power of titanium dioxide, an inorganic coating treatment is adopted in the titanium dioxide production process. In this invention, the attapulgite-coated titanium dioxide uses inorganic coating slurry after inorganic coating treatment as raw material.

[0023] Specifically, the inorganic coating process for titanium dioxide is as follows: Take a milled titanium dioxide-based slurry (particle size 0.32-0.35 μm, mass concentration 300±5 g / L), heat it to 85℃, then add NaOH solution over 10 min, adjust the pH to 10-11, and homogenize for 20 min; then add sodium silicate solution (concentration 100 g / L) over 30 min, the amount added being 3.2% of the total TiO2 in the slurry based on total SiO2, homogenize for 20 min, then add dilute sulfuric acid at a uniform rate over 150 min, adjust the slurry pH to 7.0, homogenize for 30 min, and finally add sodium hexametaphosphate solution (concentration 40 g / L), the amount added being P2... The inorganic coating process is completed by adding 0.15% (calculated as O5) of the total TiO2 in the slurry over 20 minutes, followed by homogenization for 20 minutes. The temperature is then adjusted to 70℃, and zinc sulfate solution (90 g / L) is added concurrently with NaOH, at a rate of 1.2% (calculated as ZnO) of the total TiO2 in the slurry over 60 minutes, maintaining the pH at 6.8–7.2, and homogenizing for 30 minutes. Next, sodium aluminate solution (160 g / L) is added concurrently with 10% dilute H2SO4, at a rate of 2.0% (calculated as Al2O3) of the total TiO2 in the slurry over 90 minutes, maintaining the pH at 7.8–8.2, and homogenizing for 120 minutes. The inorganic coating process is then complete. In the titanium dioxide production process, the slurry after inorganic coating treatment is filtered, washed, dried, and then treated with steam to obtain the finished titanium dioxide product.

[0024] In the following embodiments, the inorganic coating slurry after the above inorganic coating treatment is used as raw material.

[0025] In addition, the attapulgite used in this invention to prepare titanium dioxide coated with attapulgite needs to be purified. The purification method is as follows: attapulgite and deionized water are mixed at a solid-liquid ratio of 1:10 and stirred to form a suspension. 0.5%-1.0% of dilute hydrochloric acid (5%-8% concentration hydrochloric acid) relative to the mass of attapulgite is added to the suspension. The mixture is heated to 80-90℃ and stirred at a constant temperature for 2-3 hours to remove impurities. After the reaction is completed, the mixture is filtered and washed with deionized water until the pH of the filter cake is 6-7. After drying at 105-110℃, it is pulverized to obtain purified attapulgite, which is a white powder.

[0026] In the following embodiments, the purified attapulgite clay is used as the raw material.

[0027] The sources of some of the chemicals used in the following examples and comparative examples are shown in the table below:

[0028] Example 1 Titanium dioxide coated with attapulgite was prepared using the following method.

[0029] 1. Titanate-modified attapulgite: Purified attapulgite was added to anhydrous ethanol at a solid-liquid ratio of 1:8 and ultrasonically dispersed for 30 minutes (300-500W) to form a uniform suspension. Then, 3%-5% of titanate coupling agent (chelated dioctyl pyrophosphate oxy) based on the weight of the attapulgite was added. After stirring at 60-70℃ for 1.5-2 hours, the solvent was removed by vacuum distillation (65-75℃, vacuum (-0.08)~(-0.09MPa)). The mixture was then dried at 120℃ for 2 hours and pulverized to obtain titanate-modified attapulgite. A 30% modified attapulgite suspension was prepared by adding 5‰ sodium polycarboxylate salt for later use.

[0030] 2. Composite coating of titanium dioxide with modified attapulgite: Adjust the pH of the slurry to 7.5, maintain the temperature at 65℃-70℃, and slowly add the titanium ester modified attapulgite suspension to the inorganic surface-treated titanium dioxide slurry. The amount added is 12% of the total TiO2 in the slurry based on the modified attapulgite. At the same time, turn on the ultrasonic (power 500W) to assist dispersion for 30min, maintain the pH at 7-8, and homogenize for 120min.

[0031] 3. Finally, the modified titanium dioxide slurry is filtered, washed, flash-evaporated, and steam-powdered with deionized water to obtain modified attapulgite-coated titanium dioxide.

[0032] 4. Add the coated titanium dioxide to deionized water and pure acrylic emulsion and stir to prepare a sample. According to the requirements of GB / T 25261-2018 "Reflective Thermal Insulation Coatings for Buildings", test the technical indicators of the sample, such as solar reflectance, near-infrared reflectance, and hemispherical emissivity.

[0033] like Figure 2 As shown, the reflectivity of titanium dioxide coated with attapulgite at concentrations of 0-20 wt% was compared. The 0% coating amount refers to finished titanium dioxide without attapulgite coating.

[0034] It can be seen that when the coating amount is less than 10%, the improvement in reflectivity is not significant; when the coating amount is 10-15%, the improvement in reflectivity is significant; when the coating amount exceeds 15%, the reflectivity is actually lower than that of titanium dioxide without attapulgite coating.

[0035] Comparative Examples 1 and 2 are titanium dioxide coated with attapulgite clay prepared using different coating methods. Their reflectance properties were compared with the sample in Example 1 with a coating amount of 12%.

[0036] Comparative Example 1 The difference from Example 1 is that finished titanium dioxide is used as raw material, deionized water is added to prepare titanium dioxide slurry, and then attapulgite is applied for coating. The coating process is the same as in Example 1, and the amount of attapulgite added is 12%.

[0037] Comparative Example 2 The difference from Example 1 is that the attapulgite was not modified with titanate and the suspension was prepared directly. The rest is the same as in Example 1, and the amount of attapulgite added is 12%.

[0038] Table 1 Comparison of the reflective properties of titanium dioxide

[0039] The comparison above shows that the reflectivity of Comparative Examples 1 and 2 is lower than that of the finished titanium dioxide. This is presumably because the attapulgite clay did not effectively coat the titanium dioxide.

[0040] Example 2 Titanium dioxide coated with attapulgite clay (12% coating weight) prepared in Example 1 was used. Following Formula 1, 16.2 parts of deionized water were added to a mixing container. Under medium-low speed stirring, 0.25 parts of PLUS330 cellulose, 0.6 parts of 5040 dispersant, 0.2 parts of wetting agent, 0.25 parts of 3157 defoamer, and 1.5 parts of dodecyl film-forming agent were added sequentially. After stirring until homogeneous, the speed was increased, and 6 parts of NF-100 crack-resistant additive, 8.0 parts of hydrophobic modified aerogel, graded hollow glass microspheres (HL25 and HL15 mixed in a 1:1 ratio), 18 parts of composite modified reflective pigment, 4 parts of modified precipitated barium sulfate, and 0.2 parts of pH adjuster were added sequentially. The mixture was dispersed at high speed (2000-2500 r / min) until homogeneous, then the speed was reduced to 600-600 r / min. Add 35 parts of pure acrylic emulsion, 0.3 parts of A10 defoamer, 0.35 parts of bactericide and preservative, and 0.35 parts of leveling agent at 900 r / min, and stir evenly to obtain heat-insulating and reflective coating.

[0041] Example 3 Formula 2 was used, and the remaining processes were the same as in Example 2.

[0042] Example 4 Formula 3 was used, and the remaining processes were the same as in Example 2.

[0043] Comparative Example 3 Titanium dioxide was coated with attapulgite clay prepared in Comparative Example 1, and the remaining process formulation was the same as in Example 2.

[0044] Comparative Example 4 Titanium dioxide was coated with attapulgite clay prepared in Comparative Example 2, and the remaining process formulation was the same as in Example 3.

[0045] Comparative Example 5 Take the finished titanium dioxide, and the rest of the process formula is the same as in Example 4.

[0046] Table 2 Experimental Formulation of Reflective Heat Insulation Coating

[0047] The performance of the reflective heat-insulating coatings prepared in the three examples (Examples 4-6) and three comparative examples (Comparative Examples 4-6) was tested, and the results are shown in Table 2. The thermal conductivity, solar reflectance, near-infrared reflectance, hemispherical emissivity, rate of change of solar reflectance after pollution, and thermal insulation temperature difference with the reference blackboard were tested according to the requirements of GB / T 25261-2018 "Reflective Heat-Insulating Coatings for Buildings". The "resistance to artificial weathering and water resistance" technical indicators were tested according to the requirements of GB / T 9755-2024 "Synthetic Resin Emulsion Wall Coatings".

[0048] Table 3 Performance Evaluation Results of Reflective Thermal Insulation Coatings

[0049] The data in Table 2 show that the reflective heat-insulating coatings prepared in Examples 1-3 have high solar reflectivity (visible light ≥90%, near-infrared ≥90%), a heat insulation temperature difference of more than 30°C with the reference blackboard, excellent weather resistance (no abnormalities after 2000h of artificial climate aging), and 240h of water resistance. In Comparative Example 1, after replacing the modified attapulgite composite modified reflective pigment prepared in this invention with general infrared reflective titanium dioxide, the solar reflectivity, heat insulation temperature difference, weather resistance, and water resistance were significantly reduced. In Comparative Examples 2 to 4, hydrophobic modified aerogel and hierarchical hollow microspheres were added either not or only partially, and their solar reflectivity, heat insulation temperature difference, weather resistance, and water resistance were all reduced to varying degrees.

[0050] In summary, the reflective heat-insulating coating of this invention exhibits good stability and is suitable for multiple application scenarios. It can meet the requirements for infrared reflective cooling while also balancing the stability and economy of the coating / product. Furthermore, the process is simple to operate and suitable for industrial-scale promotion and application.

Claims

1. A method for preparing an attapulgite-coated titanium white powder, characterized in that, The method comprises the following steps: S1, removing impurities from the attapulgite by hydrochloric acid treatment to obtain purified attapulgite, and then performing surface modification treatment on the purified attapulgite by using a titanate coupling agent to obtain modified attapulgite; S2, mixing the modified attapulgite with deionized water to prepare a suspension, and then mixing the suspension with a titanium dioxide inorganic coating slurry to obtain a mixed slurry; S3, filtering, washing, flash evaporating and powdering the mixed slurry to obtain the attapulgite-coated titanium dioxide.

2. The method of claim 1, wherein the coated attapulgite titanium dioxide pigment is prepared by the steps of: In step S2, the amount of the modified attapulgite added is 10-15% of the mass of the titanium dioxide in the inorganic coating slurry.

3. The method for preparing attapulgite-coated titanium dioxide according to claim 1, characterized in that, In step S2, the solid content of the suspension is 50wt%, and 5wt% of sodium polycarboxylate is added to the suspension.

4. The method of claim 1, wherein the coated attapulgite titanium dioxide pigment is prepared by the steps of: In step S1, the surface modification treatment is performed by adding the purified attapulgite into an alcohol solvent to form a suspension after dispersion, then adding 3-5% of the mass of the purified attapulgite into a titanate coupling agent, stirring at a constant temperature of 60-70°C for 1.5-2h, removing the solvent by reduced pressure distillation, and drying and crushing to obtain the titanate-modified attapulgite.

5. The method for preparing attapulgite-coated titanium dioxide according to claim 4, characterized in that, The alcohol solvent is anhydrous ethanol or isopropyl alcohol.

6. The attapulgite-coated titanium dioxide prepared by the preparation method of any one of claims 1-5.

7. A reflective thermal barrier coating characterized by, The composition comprises the following components in parts by weight: deionized water 10-20 parts, hydrophobically modified cellulose 0.2-0.4 parts, additives 2-5 parts, modified silica aerogel 6-12 parts, graded hollow microbeads 6-10 parts, nano anti-cracking additive 5-8 parts, attapulgite-coated titanium dioxide 15-25 parts, modified barium sulfate 3-8 parts, pure acrylic emulsion 25-45 parts, thickening agent 0.3-0.5 parts, and the attapulgite-coated titanium dioxide is as described in claim 6.

8. The reflective thermal barrier coating of claim 7, wherein, The additives include wetting agents, dispersants, defoaming agents, film-forming agents, antifreezing agents, and bactericidal preservatives.

9. The method of claim 8, wherein the reflective thermal barrier coating is prepared by, The method comprises the following steps: S11, adding deionized water into a stirring device, and then adding hydrophobically modified cellulose into the stirring device while stirring, adding wetting agents, dispersants, defoaming agents and film-forming agents after the hydrophobically modified cellulose is dissolved, and stirring uniformly, S12, adding nano anti-cracking additive, modified silica aerogel, graded hollow microbeads, attapulgite-coated titanium dioxide, modified barium sulfate and pH adjuster in sequence, stirring at high speed until the dispersion is less than or equal to 50μm, and then adding pure acrylic emulsion, defoaming agent, antifreezing agent, bactericidal preservative and thickening agent, and stirring uniformly to obtain the product.

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