Modified calcium silicate, preparation method and application thereof, and coating

Abstract

The invention provides modified calcium silicate, a preparation method and application thereof and a coating, and belongs to the technical field of coatings. The preparation method comprises the following steps: mixing a Na2SiO3 solution, a Ca (OH) 2 solution, a modifier and water, and carrying out hydrothermal modification to obtain the modified calcium silicate. According to the invention, the modifier increases the lipophilicity and dispersity of calcium silicate, improves the compatibility of calcium silicate with the coating, and further optimizes the mechanical properties of the coating, and the coating formed by the prepared coating has good adhesive force and mechanical properties. The hydrothermal modification parameters are further limited, the crystallization degree and the deagglomeration of the modified calcium silicate are improved by increasing the temperature, the crystal growth can be optimized by prolonging the reaction time of the hydrothermal modification, but secondary agglomeration can be caused by overlong reaction time, uniform mixing is ensured by the rotating speed, and the phase composition of the product is influenced by the Ca / Si molar ratio. And the Na2SiO3 solution is limited to be obtained from high-silicon solid waste, so that the dual goals of high-value utilization of the solid waste and reduction of the coating cost are achieved.

Description

Technical Field

[0001] This invention relates to the field of coating technology, and in particular to a modified calcium silicate, its preparation method and application, and coatings. Background Technology

[0002] Inorganic environmentally friendly coatings have become a research hotspot in the coatings field in recent years due to their low VOC (volatile organic compounds), non-toxicity, and strong weather resistance. Currently, the technology system for developing inorganic environmentally friendly coatings is gradually maturing. This includes water-based inorganic coatings synthesized from film-forming substances such as silicates, silica sols, and phosphates, which are widely used in building exterior walls; coatings that enhance antibacterial, self-cleaning, and wear-resistant properties by adding nano-SiO2 and TiO2; and inorganic-organic hybrid systems that combine the durability of inorganic materials with the flexibility of organic materials (such as silicone-acrylic emulsion composite coatings). However, the proportion of organic components must be strictly controlled to maintain environmental friendliness. In terms of environmental performance, inorganic coatings do not require organic solvents, meeting environmental standards. Furthermore, inorganic film-forming substances are resistant to high temperatures, ultraviolet rays, and acids and alkalis, with a lifespan of 15-20 years (compared to approximately 5-10 years for traditional latex paint), making them suitable for tunnels, steel structures, and other applications. They can also replace some epoxy resin coatings in applications such as ships and bridges (e.g., water-based inorganic zinc-rich coatings, functional coatings, radiation cooling coatings, and anti-mildew coatings).

[0003] Calcium silicate is an inorganic compound composed of calcium, silicon, and oxygen. It is abundant in nature (such as in minerals) and is also industrially produced in various grades, widely used in cement, coatings, and insulation materials. The structural unit of calcium silicate is the silicon-oxygen tetrahedron, exhibiting a chain-like structure with numerous micropores. Due to its loose, porous structure, high specific surface area, and good thermal stability and mechanical properties, it has attracted widespread attention both domestically and internationally. Furthermore, calcium silicate possesses excellent biocompatibility, chemical stability, and mechanical properties, making it widely applicable in building materials, biomedicine, and environmental remediation. However, current technologies for calcium silicate suffer from problems such as easy aggregation and poor compatibility with organic matrices, limiting its applications. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a modified calcium silicate, its preparation method and application, and coatings. The modified calcium silicate prepared by this invention has good dispersibility and good compatibility with organic matrices, and the coatings formed by the prepared calcium silicate have good adhesion and mechanical properties.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing modified calcium silicate, comprising the following steps: The modified calcium silicate is obtained by hydrothermal modification of Na2SiO3 solution, Ca(OH)2 solution, modifier and water. The modifier includes one or more of polyethylene glycol (PEG), stearic acid, sodium stearate, triethanolamine and liquid paraffin.

[0006] Preferably, the hydrothermal modification time is 35-70 minutes and the temperature is 80-95°C.

[0007] Preferably, the molar ratio of Ca in the Ca(OH)2 solution to Si in the Na2SiO3 solution (Ca / Si molar ratio) is 0.8~1.8:1.

[0008] Preferably, the mass of the polyethylene glycol is 1 to 1.7 wt% of the Na2SiO3 in the Na2SiO3 solution.

[0009] Preferably, the hydrothermal modification is carried out under stirring, and the stirring speed is 500~800 r / min.

[0010] Preferably, the Na2SiO3 solution is obtained from high-silicon solid waste, which includes one or more of microsilica powder, high-silica fly ash, and coal gangue.

[0011] The present invention also provides modified calcium silicate prepared by the preparation method described in the above technical solution.

[0012] This invention also provides the application of the modified calcium silicate described in the above technical solution in the field of coatings.

[0013] The present invention also provides a coating comprising the modified calcium silicate, titanium dioxide, heavy calcium carbonate, kaolin, styrene-acrylic emulsion, additives and water as described in the above technical solution; wherein the additives include dispersants, wetting agents, propylene glycol, leveling agents, film-forming aids, defoamers, preservatives, thickeners and cellulose.

[0014] Preferably, the mass percentage of modified calcium silicate in the coating is 11.3 to 30.1%, based on the amount of wetting modified calcium silicate.

[0015] This invention provides a method for preparing modified calcium silicate, comprising the following steps: mixing Na2SiO3 solution, Ca(OH)2 solution, modifier and water for hydrothermal modification to obtain the modified calcium silicate, wherein the modifier includes one or more of PEG, stearic acid, sodium stearate, triethanolamine and liquid paraffin.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention utilizes a modifier to increase the oleophilicity and dispersibility of calcium silicate, thereby improving its compatibility with coatings and optimizing the mechanical properties of the coatings. The resulting coating exhibits excellent adhesion and mechanical properties. Furthermore, this invention employs a method of simultaneously synthesizing and modifying calcium silicate, which improves production efficiency compared to the traditional method of preparing first and then modifying. Ultimately, it yields modified calcium silicate with good dispersibility and compatibility with organic matrices.

[0017] Furthermore, this invention defines the parameters for hydrothermal modification. Increasing the temperature helps to improve the crystallinity (increase whiteness) and deagglomerate (reduce particle size) of modified calcium silicate. Extending the reaction time of hydrothermal modification can optimize crystal growth, but too long a reaction time can lead to secondary agglomeration. Rotation speed ensures uniform mixing. The Ca / Si molar ratio affects the phase composition of the product. The amount of modifier effectively improves the powder dispersibility and further reduces the oil absorption value.

[0018] Data from the examples show that the modified calcium silicate prepared by the present invention has a whiteness of 92.3%, an oil absorption value of 70 mL / 100 g, a particle size D50 of 5.76 μm, and a D90 of 9.22 μm.

[0019] Furthermore, this invention specifies that the Na2SiO3 solution is obtained from high-silicon solid waste, achieving the dual goals of high-value utilization of solid waste and reducing coating costs.

[0020] The present invention also provides a coating comprising the modified calcium silicate described in the above technical solution. The coating has a uniform and stable fluid state, good hiding power, and the formed coating has a strong "neck connection" multi-level porous network structure with good adhesion and mechanical properties. Attached Figure Description

[0021] Figure 1 The whiteness curves of the modified calcium silicate prepared in Examples 1 and 2 are shown. Figure 2 The oil absorption curves are for the modified calcium silicate prepared in Examples 1 and 2. Figure 3 The particle size D50 curves of the modified calcium silicate prepared in Examples 1 and 2 are shown. Figure 4 The whiteness curves of the modified calcium silicate prepared in Examples 1 and 3 are shown. Figure 5 The oil absorption curves are for the modified calcium silicate prepared in Examples 1 and 3. Figure 6 The particle size D50 curves of the modified calcium silicate prepared in Examples 1 and 3 are shown. Figure 7 The whiteness curves of the modified calcium silicate prepared in Examples 1 and 4 are shown. Figure 8Oil absorption curves of the modified calcium silicate prepared in Examples 1 and 4; Figure 9 The particle size D50 curves of the modified calcium silicate prepared in Examples 1 and 4 are shown. Figure 10 Whiteness curves of the modified calcium silicate prepared in Examples 1 and 5; Figure 11 Oil absorption curves of the modified calcium silicate prepared in Examples 1 and 5; Figure 12 The particle size D50 curves of the modified calcium silicate prepared in Examples 1 and 5 are shown. Figure 13 This is a diagram showing the average particle size distribution of dry-process calcium silicate powder. Figure 14 The average particle size distribution of the modified calcium silicate prepared in Example 1 is shown in the figure. Figure 15 The images show actual test results of the coating reflectance (CR) of Comparative Example 3, Comparative Example 2, and Example 6. Figure 16 The images show actual test results of the coating reflectance of Examples 7, 8, and Comparative Example 4. Figure 17 The particle size comparison curves are for the coatings prepared in Examples 6-8 and Comparative Example 4. Figure 18 The pH value comparison curves are for the coatings prepared in Examples 6-8 and Comparative Example 4. Figure 19 Viscosity change curves of coatings prepared in the examples and comparative examples at different standing times; Figures 20-23 The SEM images of the coating cross-section at different magnifications are provided by [the source]. Figures 20 to 23 The magnification gradually increases; Figure 24 The average particle size distribution of the modified calcium silicate prepared in Example 9 is shown in the diagram. Figure 25 The average particle size distribution of the modified calcium silicate obtained in Example 10 is shown in the diagram. Figure 26 This is a diagram showing the average particle size distribution of the modified calcium silicate obtained in Example 11; Figure 27 The image shows the average particle size distribution of the modified calcium silicate prepared in Example 12. Detailed Implementation

[0022] This invention provides a method for preparing modified calcium silicate, comprising the following steps: The modified calcium silicate is obtained by hydrothermal modification of Na2SiO3 solution, Ca(OH)2 solution, modifier and water. The modifier includes one or more of PEG, stearic acid, sodium stearate, triethanolamine and liquid paraffin.

[0023] Unless otherwise specified, all raw materials used in this invention are commercially available products in the field.

[0024] In this invention, the Na2SiO3 solution is preferably obtained from high-silicon solid waste, which includes one or more of microsilica powder, high-silica fly ash, and coal gangue, and more preferably is obtained from microsilica powder through an alkaline hydrothermal extraction method. This invention uses high-silica solid waste as raw material, achieving the dual goals of high-value utilization of solid waste and reduction of coating costs.

[0025] In this invention, the SiO2 content in the Na2SiO3 solution is preferably 85~86wt%, and the modulus is preferably 2.73~2.75. In specific embodiments of this invention, there are no special limitations on the specific parameters of the alkaline hydrothermal extraction method, and methods well known to those skilled in the art can be used.

[0026] In this invention, the Ca(OH)₂ solution is preferably obtained by dissolving quicklime in water. This invention does not impose any particular limitation on the concentration of the Ca(OH)₂ solution.

[0027] In this invention, the molar ratio of Ca in the Ca(OH)2 solution to Si in the Na2SiO3 solution is preferably 0.8 to 1.8:1, specifically 0.8:1, 1:1, 1.2:1, 1.4:1, 1.6:1 or 1.8:1.

[0028] In this invention, the hydrothermal modification time is preferably 35-70 min, specifically 35, 40, 45, 50, 55, 60, 65 or 70 min, and the temperature is preferably 80-95℃, specifically 80, 83, 86, 89, 92 or 95℃.

[0029] In this invention, the mass of the modifier is preferably 1 to 1.7 wt% of Na2SiO3 in the Na2SiO3 solution, specifically 1 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, or 1.7 wt%.

[0030] In this invention, the number-average molecular weight of the PEG is preferably 400 to 8000.

[0031] In this invention, the number-average molecular weight of the liquid paraffin is preferably 150-250.

[0032] In this invention, the hydrothermal modification is preferably carried out under stirring, and the stirring speed is preferably 500~800 r / min, specifically 500, 600, 700 or 800 r / min.

[0033] In this invention, the Na2SiO3 solution is preferably diluted with water, heated to a specified temperature (preferably 55~60℃) in a water bath, and then the Ca(OH)2 solution is added for water bath heating while a modifier is added to perform the hydrothermal modification.

[0034] After the hydrothermal modification is completed, the resulting solution is preferably filtered and then washed with deionized water to obtain the modified calcium silicate.

[0035] In this invention, the modified calcium silicate is preferably used directly in the form of modified calcium silicate filter cake to prepare the coating. The moisture content of the modified calcium silicate filter cake is preferably 1~70wt%, specifically 1.45wt% or 66.01wt%. Using the modified calcium silicate filter cake directly in the coating preparation eliminates the drying and grinding steps, simplifying the process. Moreover, the amount of modified calcium silicate added can significantly affect the coating performance, keeping the pH value of the coating below 9, ensuring a uniform and stable fluid state, good hiding effect, and forming a strong neck-connected multi-level porous network structure on the coating cross-section, resulting in good adhesion and mechanical properties.

[0036] The hydrothermal modification process of this invention is simple, has low reaction energy consumption, does not generate secondary solid waste, and can reduce the total cost. The modified calcium silicate product obtained has high whiteness, small particle size, and effectively improves powder dispersibility and reduces oil absorption value.

[0037] The present invention also provides modified calcium silicate prepared by the preparation method described in the above technical solution.

[0038] This invention also provides the application of the modified calcium silicate described in the above technical solution in the field of coatings.

[0039] The present invention also provides a coating comprising the modified calcium silicate, titanium dioxide, heavy calcium carbonate, kaolin, styrene-acrylic emulsion, additives and solvents described in the above technical solution.

[0040] In this invention, the mass percentage of modified calcium silicate in the coating, based on the wetted modified calcium silicate (i.e., the modified calcium silicate filter cake), is preferably 11.3% to 30.1%, specifically 11.3%, 12.8%, 18.8%, or 30.1%. Coatings prepared using calcium silicate as an additive exhibit strong durability, reducing the frequency of renovations and thus lowering overall costs. From a post-construction cleaning and maintenance perspective, its dense surface prevents stain penetration, facilitating cleaning and providing good wear resistance, making it a preferred choice for sustainable construction, especially suitable for projects prioritizing health, safety, and long-term performance.

[0041] In this invention, the mass percentage of titanium dioxide in the coating is preferably 8.5-17.5%, specifically 8.5%, 11.1%, 14.9% or 17.5%.

[0042] In this invention, the mass percentage of heavy calcium carbonate in the coating is preferably 15-15.2%, specifically 15%.

[0043] In this invention, the mass percentage of kaolin in the coating is preferably 4 to 4.2%, specifically 4.2%.

[0044] In this invention, the mass percentage of styrene-acrylic emulsion in the coating is preferably 15.2% to 15.4%, specifically 15.4%. The styrene-acrylic emulsion is an aqueous dispersion, acting as an "adhesive" that binds the components together to form a continuous paint film. In a specific embodiment of this invention, the styrene-acrylic emulsion is preferably ACRONAL ECO 502.

[0045] In this invention, the additives preferably include dispersants, wetting agents, propylene glycol, leveling agents, film-forming aids, defoamers, preservatives, thickeners, and cellulose.

[0046] In this invention, the dispersant preferably includes one or more of sodium oleate, sodium polycarboxylate, and sulfate salts; the wetting agent preferably includes one or more of alkyl sulfates, alkyl sulfonates, and phosphate salts, more preferably alkylphenol formaldehyde resin polyoxyethylene ether sulfate SOPA-270; the leveling agent preferably includes polyurethane rheology modifier RM2020 and / or silicone leveling agent BP-241, more preferably purchased from Guangzhou Huixiang Chemical Co., Ltd., to delay the evaporation of moisture in the coating, allowing the coating sufficient time to spread and eliminating pinholes in the coating film; The film-forming aid preferably includes dodecyl alcohol ester and / or propylene glycol, which acts as a plasticizer, lowering the minimum film-forming temperature of the styrene-acrylic emulsion, and gradually volatilizing after film formation; the preservative preferably includes methylisothiazolinone and / or chloromethylisothiazolinone; the defoamer is preferably an organosilicone defoamer; the thickener preferably includes one or more of hydroxyethyl cellulose, hydroxypropyl cellulose, and cellulose, which provides system viscosity, improves leveling and anti-settling properties, and different thickeners can be combined to take into account both high shear and low shear viscosity, improving leveling, anti-sagging and storage stability.

[0047] In this invention, the particle size of the kaolin, heavy calcium carbonate and titanium dioxide is preferably 20~25μm.

[0048] The present invention also includes a remaining solvent, wherein the solvent preferably includes water and / or propylene glycol, wherein the water is preferably deionized water, and the propylene glycol serves as both a film-forming aid and a solvent, which can reduce the film-forming temperature, improve the performance of the coating film, and regulate the drying speed.

[0049] In a specific embodiment of the present invention, the preferred mass percentage of the dispersant in the coating is 1.2%, the preferred mass percentage of the wetting agent is 0.8%, the preferred mass percentage of propylene glycol is 0.6%, the preferred mass percentage of the leveling agent is 0.5%, the preferred mass percentage of the film-forming aid is 0.4%, the preferred mass percentage of the defoamer is 1.4%, the preferred mass percentage of the preservative is 0.2%, the preferred mass percentage of the thickener (excluding cellulose) is 0.2%, and the preferred mass percentage of cellulose is 0.3%.

[0050] The present invention also provides a method for preparing the coating described in the above technical solution, comprising the following steps: mixing the modified calcium silicate filter cake, titanium dioxide, heavy calcium carbonate, kaolin, styrene-acrylic emulsion, additives and solvent to obtain the coating.

[0051] In this invention, the solvent is weighed and placed in a dispersion container. After adding the dispersant and wetting agent, it is dispersed at a low speed (specifically 500 r / min) for 10 minutes. Then, kaolin, heavy calcium carbonate, titanium dioxide, and modified calcium silicate filter cake are added in sequence. The feeding process is carried out slowly. Otherwise, on the one hand, it will cause the powder to scatter during the stirring process. On the other hand, since the powder (including kaolin, heavy calcium carbonate, and titanium dioxide) has a small particle size and a large specific surface area, adding it too quickly will cause the slurry to be too viscous, which will have an adverse effect on stirring. After the feeding is completed, it is dispersed at a high speed (specifically 1200 r / min) for 30 minutes. The styrene-acrylic emulsion and other additives are added to the slurry while stirring. After stirring at a low speed (specifically 500 r / min) for 20 minutes, stirring is stopped. The stirred slurry is transferred to a container and allowed to stand to obtain the coating. The stirring speed must be strictly controlled during the stirring process to prevent the formation of a large number of air bubbles in the slurry due to excessive speed, which will affect the application performance of the coating.

[0052] During the settling process, viscosity tests and state observations are preferably conducted at 24h, 48h, 72h, and 15 days to determine whether the coating exhibits storage problems such as thickening, flocculation, or stratification.

[0053] In this invention, the dispersion container is preferably equipped with a temperature control device. In summer, indoor ventilation and cooling can be strengthened during the stirring process; in winter, the stirring process needs to be heated to 25~30℃ to facilitate the dispersion and dissolution of the solute.

[0054] In this invention, the material of the dispersion container is preferably a non-metallic corrosion-resistant stirring vessel, more preferably an enamel stirring vessel, a stainless steel stirring vessel, or a polypropylene stirring vessel, and the interior of the dispersion container preferably has an anti-rust coating or is coated with anti-rust paint.

[0055] In this invention, the cellulose and thickener are preferably added last; otherwise, the remaining components will not be easily dispersed in the coating system.

[0056] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0057] In the embodiments and comparative examples of this invention: The Na2SiO3 solution was obtained by extracting microsilica powder using an alkaline hydrothermal method. The SiO2 content in the Na2SiO3 solution was 88.6 wt%, and the modulus was 2.75. The number-average molecular weight of PEG is 400; The number-average molecular weight of liquid paraffin is 150; The dispersant is sodium polycarboxylate dispersant 5040, the wetting agent is alkylphenol formaldehyde resin polyoxyethylene ether sulfate SOPA-270, the leveling agent is polyurethane rheology modifier RM2020, the film-forming aid is alcohol ester dodecyl, the defoamer is silicone defoamer (Dow Corning AFE-1410), the preservative is methylisothiazolinone, the thickener is hydroxypropyl cellulose, and the styrene-acrylic emulsion is ACRONAL ECO 502.

[0058] Example 1 First, the Na₂SiO₃ solution was diluted with water at a mass ratio of 1:5, and then heated to a specified temperature (60℃) in a water bath. Ca(OH)₂ solution was added, maintaining a Ca / Si molar ratio of 1:1. PEG was added simultaneously with water bath heating, at an amount equal to 1% of the mass of Na₂SiO₃ in the solution. Hydrothermal modification was then performed at a reaction time of 60 min, a temperature of 95℃, and a rotation speed of 700 r / min. After the reaction was complete, the solution was filtered and washed with deionized water to obtain modified calcium silicate, i.e., modified calcium silicate filter cake. The modified calcium silicate filter cake had a water content of 66.01% and a specific surface area of ​​29.41 m². 2 / g.

[0059] Example 2 Same as Example 1, except that the hydrothermal modification reaction time was adjusted to 35, 40, 45, 50, 55, 65 or 70 min.

[0060] Figure 1 The whiteness curves are for the modified calcium silicate prepared in Examples 1 and 2. Figure 2 The oil absorption curves are for the modified calcium silicate prepared in Examples 1 and 2. Figure 3The particle size D50 curves of the modified calcium silicate prepared in Examples 1 and 2 show that as the reaction time gradually increases, the whiteness of calcium silicate reaches its highest value of 92.3% at a reaction time of 60 min. Subsequently, as the reaction time continues to increase, the whiteness of calcium silicate begins to decrease. This is because as the reaction time extends, organic impurities or unreacted components in the silicon and calcium sources are gradually consumed or decomposed, increasing the purity of the product and reducing the absorption or scattering of light by impurities, thereby improving the whiteness. The change in oil absorption value is due to the continuous increase in the crystallinity of calcium silicate particles and the continuous reduction in surface porosity and roughness, resulting in a monotonous decrease in oil absorption value. On the other hand, the surface lipophilic groups (such as -OH) may be covered by hydrophobic groups, further reducing oil absorption. Overall, the oil absorption value decreases with the increase of reaction time, reaching a minimum of 66 mL / 100 g at 65 min and then remaining stable.

[0061] Example 3 Same as Example 1, except that the temperature of the hydrothermal modification reaction was adjusted to 80, 83, 86, 89 or 92°C.

[0062] Figure 4 The whiteness curves are for the modified calcium silicate prepared in Examples 1 and 3. Figure 5 The oil absorption curves are for the modified calcium silicate prepared in Examples 1 and 3. Figure 6 The particle size D50 curves of the modified calcium silicate prepared in Examples 1 and 3 show that the whiteness of calcium silicate increases with increasing reaction temperature, reaching a maximum of 92.3% at a reaction temperature of 95℃. The oil absorption value decreases with increasing reaction temperature, reaching a minimum of 70 mL / 100 g at 92℃, and then tends to stabilize with further increases in temperature. The pH value decreases due to accelerated Ca2+ uptake at high temperatures. 2+ Hydrolysis, with its slow increase, enhances the alkalinity of the system. Whiteness increases with increasing reaction temperature due to improved crystallinity; high temperatures promote perfect crystal growth, reducing light scattering defects at grain boundaries and resulting in a more uniform white color (similar to the whiteness-enhancing effect of ceramic sintering). Oil absorption decreases with increasing reaction temperature because the surface energy decreases with temperature, causing condensation of surface hydroxyl groups (-OH), reducing polar adsorption sites, and particle melting and rearrangement (minimizing surface energy), thus reducing porosity and roughness.

[0063] Example 4 Same as Example 1, except that the Ca / Si molar ratio was adjusted to 0.8:1, 1.2:1, 1.4:1, 1.6:1 or 1.8:1.

[0064] Figure 7 The whiteness curves are for the modified calcium silicate prepared in Examples 1 and 4. Figure 8 The oil absorption curves are for the modified calcium silicate prepared in Examples 1 and 4. Figure 9 The particle size D50 curves for the modified calcium silicate prepared in Examples 1 and 4 show that lower Ca / Si molar ratios tend to produce amorphous silica or low-calcium silicates (such as CSH gels) because of residual unreacted SiO2 or Fe. 3+ Impurities reduce whiteness. Increasing the Ca / Si molar ratio promotes the formation of crystalline calcium silicate (such as wollastonite CaSiO3). Increased crystallinity reduces surface defects and impurity adsorption, generally resulting in higher whiteness. However, excess Ca(OH)2 residue may introduce trace amounts of Mg ions due to the alkaline environment. 2+ Al 3+ This reduces whiteness. Therefore, when Ca / Si = 1:1, the crystals are complete and there are few impurities, resulting in the highest whiteness. Well-crystallized calcium silicate has a smooth surface and few pores. As the Ca / Si molar ratio in the raw material increases, its oil absorption value decreases. However, excessive Ca(OH)2 will increase the oil absorption value due to the hydrophilicity of the particle surface.

[0065] Example 5 Same as Example 1, except that the amount of PEG added was adjusted to 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, or 1.7wt% of Na2SiO3 in the Na2SiO3 solution.

[0066] Figure 10 The whiteness curves are for the modified calcium silicate prepared in Examples 1 and 5. Figure 11 The oil absorption curves are for the modified calcium silicate prepared in Examples 1 and 5. Figure 12 The particle size D50 curves of the modified calcium silicate obtained in Examples 1 and 5 are shown. Compared with the unmodified dry-synthesized calcium silicate product, both are improved, indicating the feasibility of the wet-synthesized modified calcium silicate method.

[0067] Comparative Example 1 Na2SiO3 solution and Ca(OH)2 solution were subjected to a hydrothermal synthesis reaction at 95℃ for 60 min, followed by filtration, washing, drying, and grinding to obtain dry-processed calcium silicate powder with a water content of 1.45%, whiteness of 88.6%, oil absorption value of 103 mL / 100 g, particle size D50 of 14.92 μm, and D90 of 47.97 μm.

[0068] Figure 13 This is a diagram showing the average particle size distribution of dry-process calcium silicate powder. Figure 14 The image shows the average particle size distribution of the modified calcium silicate prepared in Example 1. It can be seen that after hydrothermal modification, the average particle size is significantly reduced, and the differential distribution shows a normal distribution curve.

[0069] Example 6 A coating comprising the following components by weight percentage: Deionized water 26.1%, styrene-acrylic emulsion 15.4%, heavy calcium carbonate 15.0%, modified calcium silicate filter cake from Example 1 18.8% (actual usage was 188.29g), titanium dioxide 14.9%, kaolin 4.2%, dispersant 1.2%, wetting agent 0.8%, propylene glycol 0.6%, leveling agent 0.5%, film-forming aid 0.4%, defoamer 1.4%, preservative 0.2%, thickener 0.2%, cellulose 0.3%.

[0070] The preparation method includes the following steps: According to the formula, accurately weigh water and place it in a dispersion container. Add dispersant and wetting agent, then start the FS400-D experimental dispersion mill at low speed (500 r / min) for 10 minutes. Then, add kaolin, heavy calcium carbonate, titanium dioxide, and modified calcium silicate filter cake in sequence, with the feeding process proceeding slowly. After the feeding process is complete, perform high-speed stirring dispersion, adjusting the speed of the FS400-D experimental dispersion mill to 1200 r / min for 30 minutes. While stirring, add the weighed styrene-acrylic emulsion and other additives to the high-speed dispersed slurry. Add the thickener and cellulose last, and stir at low speed (500 r / min) for 20 minutes, then stop stirring. Transfer the stirred slurry to a container and let it stand for a period of time to obtain the coating. During the standing process, viscosity tests and condition observations should be performed at 24h, 48h, 72h, and 15 days.

[0071] Example 7 Same as Example 6, except that the coating includes the following components by mass percentage: The composition of the product is as follows: deionized water 31.0%, styrene-acrylic emulsion 15.4%, heavy calcium carbonate 15.0%, modified calcium silicate filter cake from Example 1 11.3% (actual usage was 112.97g), titanium dioxide 17.5%, kaolin 4.2%, dispersant 1.2%, wetting agent 0.8%, propylene glycol 0.6%, leveling agent 0.5%, film-forming aid 0.4%, defoamer 1.4%, preservative 0.2%, thickener 0.2%, and cellulose 0.3%.

[0072] Example 8 Same as Example 6, except that the coating includes the following components by mass percentage: Deionized water 18.6%, styrene-acrylic emulsion 15.4%, heavy calcium carbonate 15.0%, modified calcium silicate filter cake from Example 1 30.1% (actual usage 301.27g), titanium dioxide 11.1%, kaolin 4.2%, dispersant 1.2%, wetting agent 0.8%, propylene glycol 0.6%, leveling agent 0.5%, film-forming agent 0.4%, defoamer 1.4%, preservative 0.2%, thickener 0.2%, cellulose 0.3%.

[0073] Comparative Example 2 Same as Example 6, except that the coating includes the following components by mass percentage: The composition of the product is as follows: deionized water 38.5%, styrene-acrylic emulsion 15.4%, heavy calcium carbonate 15.0%, dry-process calcium silicate powder of Comparative Example 1 12.8% (actual usage was 128g), titanium dioxide 8.5%, kaolin 4.2%, dispersant 1.2%, wetting agent 0.8%, propylene glycol 0.6%, leveling agent 0.5%, film-forming agent 0.4%, defoamer 1.4%, preservative 0.2%, thickener 0.2%, and cellulose 0.3%.

[0074] Comparative Example 3 Same as Example 6, except that the coating includes the following components by mass percentage: Deionized water 38.5%, styrene-acrylic emulsion 15.4%, heavy calcium carbonate 15.0%, titanium dioxide 21.3%, kaolin 4.2%, dispersant 1.2%, wetting agent 0.8%, propylene glycol 0.6%, leveling agent 0.5%, film-forming agent 0.4%, defoamer 1.4%, preservative 0.2%, thickener 0.2%, cellulose 0.3%.

[0075] Comparative Example 4 Same as Example 6, except that the coating includes the following components by mass percentage: Deionized water 26.1%, styrene-acrylic emulsion 15.4%, heavy calcium carbonate 15.0%, unmodified calcium silicate filter cake 18.8% (actual usage 188.29g), titanium dioxide 14.9%, kaolin 4.2%, dispersant 1.2%, wetting agent 0.8%, propylene glycol 0.6%, leveling agent 0.5%, film-forming agent 0.4%, defoamer 1.4%, preservative 0.2%, thickener 0.2%, cellulose 0.3%.

[0076] The preparation method of the unmodified calcium silicate filter cake is the same as that in Example 1, except that polyethylene glycol is not added. The resulting unmodified calcium silicate filter cake has a moisture content of 66.01%.

[0077] Figure 15 The images show actual test results of the coating reflectance (CR) of Comparative Example 3, Comparative Example 2, and Example 6. Figure 16The images shown are actual test results of the coatings prepared in Examples 7, 8, and Comparative Example 4. Table 1 shows the test results of the coatings prepared in the examples and comparative examples. It can be seen that the coating prepared in Example 6 has the best effect, and its reflectance can reach the level of dry preparation and is close to the reflectance of titanium dioxide. The reflectance of Example 6 is significantly higher than that of Examples 7 and 8. In particular, the coating prepared in Example 8 showed uneven particles after application. The coating prepared in Example 8 also showed significantly lower hiding power and uneven application. The modified calcium silicate of the present invention has significantly better hiding power than the calcium silicate prepared in the comparative example.

[0078] Table 1. Reflectance of coatings prepared in the examples and comparative examples

[0079] Figure 17 The particle size comparison curves of the coatings prepared in Examples 6-8 and Comparative Example 4 show that as the amount of modified calcium silicate added to the coating increases, the particle size of the coating shows an increasing trend. The mechanism is that modified calcium silicate, as a functional filler, directly affects the CPVC (critical pigment volume concentration) of the coating when its addition amount is close to or exceeds the CPVC. When the CPVC is close to or exceeds the CPVC, the base material in the system is not enough to completely coat and separate all the filler particles, resulting in direct contact and aggregation between particles, which ultimately manifests as an increase in particle size.

[0080] Figure 18 The pH value comparison curves of the coatings prepared in Examples 6-8 and Comparative Example 4 show that the pH value of the coatings continuously increases with the increase of the amount of modified calcium silicate added. The pH value of the coating in Example 7 is 8.35; when the amount added increases to 188.29g, the pH value of the coating in Example 6 is 8.73. This indicates that modified calcium silicate, as an alkaline additive, can increase the alkalinity of the coating system. This is because calcium silicate itself is alkaline, and when it is dispersed in the coating, it undergoes a slight dissolution or hydration reaction, releasing OH-. - The addition of ions leads to an increase in the pH value of the entire system. Secondly, the coating system has a certain pH buffering capacity, meaning that when the amount added reaches a certain level, the system's ability to resist pH changes is enhanced. This is crucial for the application of coatings, implying that by controlling the amount of modified calcium silicate added, the pH value of the system can be stabilized within an ideal and narrow range. This helps optimize the coating's performance in terms of corrosion prevention and storage stability.

[0081] Figure 19The viscosity change curves of the coatings prepared in the examples and comparative examples at different standing times show that the amount of modified calcium silicate added has a significant impact on the coating system structure. All formulations show an increasing viscosity trend in the initial standing period, and tend to reach equilibrium after 72 hours. This indicates that the reconstruction of the internal structure of the system is basically completed, reaching a dynamic equilibrium state. The viscosity at this point can be regarded as the final stable viscosity of the formulation. When the amount of modified calcium silicate filter cake added is less than 188.29 g, the final equilibrium viscosity of the system is low and close, indicating that calcium silicate mainly plays the role of inert filler. However, when the amount of modified filter cake added increases to 301.27 g, the final viscosity increases significantly, indicating that after exceeding the critical dosage, the calcium silicate particles significantly enhance the cohesion of the system. This change in rheological behavior directly indicates that the bonding strength after curing will be substantially improved. Therefore, this trend in bonding strength meets the basic requirements of coatings.

[0082] The coating prepared in Example 6 was applied to a glass plate to obtain a coating layer.

[0083] Figures 20-23 The SEM images of the coating cross-section at different magnifications are provided by [the source]. Figures 20 to 23 As the magnification gradually increases, it can be seen that the coating has a strong neck-connected multi-level porous network structure, and good adhesion and mechanical properties.

[0084] The coating prepared in Example 6 was subjected to performance tests, and the results are shown in Table 2. If all test items meet the requirements, the product can be considered qualified. The coating of the present invention has superior performance. Among them, the scrub resistance ≥6000 is a superior grade coating, and the scrub resistance of this coating reaches 14000, which is excellent performance. Secondly, the standard for volatile organic compounds is ≤80, and the volatile organic compound content of this coating is 6, which is better than the standard. Finally, this coating also has certain advantages in terms of drying time and bonding strength. This is mainly because the modified calcium silicate component is added to the coating of the present invention, and the amount of light components (film-forming aids, leveling agents, etc.) is less, resulting in a denser system, which leads to a shorter drying time and higher bonding strength.

[0085] Table 2. Performance test results of coating in Example 6

[0086] Example 9 Same as Example 1, except that PEG is replaced with stearic acid.

[0087] Figure 24 The image shows the average particle size distribution of the modified calcium silicate prepared in Example 9.

[0088] Example 10 Same as Example 1, except that PEG is replaced with sodium stearate.

[0089] Figure 25 The image shows the average particle size distribution of the modified calcium silicate prepared in Example 10.

[0090] Example 11 Same as Example 1, except that PEG is replaced with triethanolamine.

[0091] Figure 26 The image shows the average particle size distribution of the modified calcium silicate prepared in Example 11.

[0092] Example 12 Same as Example 1, except that PEG is replaced with liquid paraffin.

[0093] Figure 27 The image shows the average particle size distribution of the modified calcium silicate prepared in Example 12.

[0094] Depend on Figures 24-27 As can be seen, the present invention uses a method of simultaneously synthesizing and modifying calcium silicate to prepare modified calcium silicate, which improves production efficiency and ultimately yields modified calcium silicate with good dispersibility.

[0095] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing modified calcium silicate, characterized in that, Includes the following steps: The modified calcium silicate is obtained by hydrothermal modification of Na2SiO3 solution, Ca(OH)2 solution, modifier and water. The modifier includes one or more of polyethylene glycol, stearic acid, sodium stearate, triethanolamine and liquid paraffin. The hydrothermal modification time is 35~70 min, and the temperature is 80~95℃; The mass of the modifier is 1 to 1.7 wt% of Na2SiO3 in the Na2SiO3 solution.

2. The preparation method according to claim 1, characterized in that, The molar ratio of Ca in the Ca(OH)2 solution to Si in the Na2SiO3 solution is 0.8~1.8:

1.

3. The preparation method according to claim 1, characterized in that, The hydrothermal modification is carried out under stirring at a speed of 500-800 r / min.

4. The preparation method according to claim 1, characterized in that, The Na2SiO3 solution is obtained from high-silicon solid waste, which includes one or more of microsilica powder, high-silica fly ash, and coal gangue.

5. Modified calcium silicate prepared by the preparation method according to any one of claims 1 to 4.

6. The application of the modified calcium silicate according to claim 5 in the field of coatings.

7. A coating, characterized in that, It includes the modified calcium silicate, titanium dioxide, heavy calcium carbonate, kaolin, styrene-acrylic emulsion, additives, and water as described in claim 5; the additives include dispersants, wetting agents, propylene glycol, leveling agents, film-forming aids, defoamers, preservatives, thickeners, and cellulose.

8. The coating according to claim 7, characterized in that, Based on the amount of wetting modified calcium silicate, the mass percentage of modified calcium silicate in the coating is 11.3~30.1%.

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