Silicon-aluminum composite coated titanium dioxide as well as preparation method and application thereof

Abstract

The invention discloses silicon-aluminum composite coated titanium dioxide and a preparation method and application thereof.The preparation method of the titanium dioxide comprises the steps that a sodium metasilicate solution and an aluminum sulfate solution are dropwise added into titanium dioxide slurry with the pH value being 7.0-8.0 at the same time for a coating reaction at the constant temperature of 60-80 DEG C, the dropwise adding time is longer than or equal to 60 min, and then the titanium dioxide slurry is subjected to a reaction for 2-3 h; in the dropwise adding process, the pH value of the reaction system is maintained at 6-8 through a buffer system. Under the condition of nearly neutral pH, a buffer system is utilized to realize collaborative deposition of silicon and aluminum components on the surface of titanium dioxide, a compact and uniform composite coating layer is formed, and the problems of unstable reaction, loose film layer, particle aggregation and the like caused by a traditional acid-base adjusting process can be effectively avoided. The preparation method is simple and convenient in process and high in process controllability, can remarkably improve the compactness and bonding strength of a coating layer so as to improve the stability and weather resistance of titanium dioxide, can be widely applied to multiple industrial fields such as coatings and plastics, and has a good application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of inorganic materials, in particular to a silicon-aluminum composite coated titanium dioxide and a preparation method and application thereof. BACKGROUND

[0002] Titanium dioxide is an important white inorganic pigment, and its main component is titanium dioxide. Due to its excellent hiding power, high whiteness and good chemical stability, it is widely used in the fields of coatings, plastics, rubber, ink and papermaking industry. However, titanium dioxide will exhibit photocatalytic activity under ultraviolet light, which may trigger the degradation reaction of surrounding organic matter, which not only reduces the aesthetic appearance of the product, but also affects its weather resistance and service life. In order to overcome this defect, the prior art usually adopts the method of coating inorganic film layer such as silicon oxide and aluminum oxide on the surface of titanium dioxide particles to shield its photocatalytic activity and improve the dispersion performance.

[0003] The mainstream titanium dioxide coating process in current industrial production is mainly based on acid-base adjustment method, that is, the pH value of the reaction system is controlled to realize the alternate deposition of silicon oxide and aluminum oxide. This method needs to accurately adjust the pH value to different ranges in stages, first depositing silicon oxide under alkaline conditions, and then depositing aluminum oxide under acidic conditions. This process not only needs to frequently adjust the acidity and alkalinity of the reaction system, but also involves multiple temperature changes and intermediate washing steps. Such multi-step operation not only leads to high energy consumption, but also makes the process control complex. More importantly, the multi-layer film formed by this method has weak interlayer bonding force, which is easy to peel off during subsequent processing or use, directly affecting the stability and weather resistance performance of the material. In addition, due to the strict requirement of traditional process on pH value control accuracy, local pH inhomogeneity is easy to occur in actual production, leading to particle agglomeration and uneven film layer deposition thickness, which not only damages the optical performance of the material, but also increases the discharge amount and processing difficulty of process wastewater, which is not conducive to realizing environment-friendly production.

[0004] In view of this, the present application is proposed. SUMMARY

[0005] The purpose of the present application is to provide a silicon-aluminum composite coated titanium dioxide and a preparation method and application thereof, so as to effectively avoid the problems of reaction instability, interface discontinuity, loose film layer and particle agglomeration caused by traditional acid-base adjustment.

[0006] The present application is realized as follows: In a first aspect, the present application provides a preparation method of a silicon-aluminum composite coated titanium dioxide, which comprises: Under the constant temperature condition of 60-80℃, the sodium metasilicate solution and the aluminum sulfate solution are simultaneously added dropwise into the titanium dioxide slurry with pH value of 7.0-8.0, the dropwise adding time is ≥60 min, and the pH value of the reaction system is maintained at 6-8 through the buffer system during the dropwise adding process.

[0007] In an alternative embodiment, the coating reaction is carried out under the constant temperature condition of 65-75℃.

[0008] In an alternative embodiment, the dropwise adding time is 60-120 min, preferably 80-100 min.

[0009] In an alternative embodiment, the concentration of the titanium dioxide slurry is 200-350 g / L, the concentration of the sodium metasilicate solution is 0.2-0.6 mol / L, and the concentration of the aluminum sulfate solution is 0.2-0.6 mol / L.

[0010] In an alternative embodiment, the molar ratio of SiO2 to Na2O in the sodium metasilicate solution is (2.5-3.5):1.

[0011] In an alternative embodiment, the mass ratio of the sodium metasilicate to the aluminum sulfate, in terms of SiO2 and Al2O3, is (2-4):1.5, and the mass ratio of the total mass of the sodium metasilicate and the aluminum sulfate to the mass of the titanium dioxide is (3.5-5.5):100.

[0012] In an alternative embodiment, the buffer system is a citrate-bicarbonate system.

[0013] In an alternative embodiment, the total mass of the citrate and the bicarbonate in the buffer system accounts for 2%-4% of the mass of the titanium dioxide.

[0014] In an alternative embodiment, the preparation step of the titanium dioxide slurry comprises: dispersing the titanium dioxide in deionized water to prepare a stable slurry, and adjusting the pH value of the system to 7-8.

[0015] In an alternative embodiment, the diluted sodium hydroxide solution is slowly added dropwise under the temperature condition of 65-75℃, the pH value of the system is adjusted to 7.0-8.0, and the system is continuously kept at temperature and stirred for 20-40 min, and further preferably the mass concentration of the sodium hydroxide solution is 10%-30%.

[0016] In an alternative embodiment, it further comprises: after the dropwise adding of the sodium metasilicate solution and the aluminum sulfate solution is completed, the system is kept at temperature for 50-70 min under the same temperature condition as the coating reaction, and a film layer densification treatment is carried out.

[0017] In an optional embodiment, the film layer densification treatment is adding a complex organic acid, adjusting the pH to 5-5.5, and continuing to age for 50-70 minutes under the same temperature conditions as in the coating reaction.

[0018] In an optional embodiment, the film layer densification treated slurry is sequentially subjected to washing, neutralization, drying, and crushing.

[0019] In an optional embodiment, the washed slurry is subjected to flash drying at a temperature of 250-270°C, and the drying time is no more than 8 seconds.

[0020] In a second aspect, the present application provides a silicon-aluminum composite coated titanium dioxide prepared by the method for preparing a silicon-aluminum composite coated titanium dioxide according to any one of the preceding embodiments.

[0021] In a third aspect, the present application provides the use of the silicon-aluminum composite coated titanium dioxide according to the preceding embodiments in a coating or plastic product.

[0022] The present application has the following beneficial effects: by using a buffer system to achieve the synergistic deposition of silicon-aluminum components on the surface of titanium dioxide under near-neutral pH conditions, a dense and uniform composite coating layer is formed, which can effectively avoid the problems of unstable reaction, discontinuous interface, loose film layer, and particle agglomeration caused by traditional acid-base adjustment processes. The method is simple and has high process controllability, which can significantly improve the denseness and bonding strength of the coating layer, thereby improving the stability and weather resistance of the titanium dioxide material. The present application can be widely applied in multiple industrial fields such as coatings and plastics, and has good application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be considered as limiting the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0024] Figure 1 Process flow diagram of the silicon-aluminum composite coated titanium dioxide according to the embodiments of the present application; Figure 2 SEM image of the silicon-aluminum composite coated titanium dioxide according to Example 1 of the present application; Figure 3 SEM image of the silicon-aluminum composite coated titanium dioxide according to Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0025] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. If specific conditions are not indicated in the embodiments, the conventional conditions or the conditions suggested by the manufacturers are adopted. If the manufacturers of the reagents or instruments are not indicated, the conventional products that can be commercially purchased are adopted.

[0026] Various embodiments of the present application can exist in the form of a range; it should be understood that the description in the form of a range is merely for the convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, it should be considered that the described range has disclosed all possible sub-ranges and single values in the range. For example, it should be considered that the range description from 1 to 6 has disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers in the described range, such as 1, 2, 3, 4, 5 and 6, which is applicable to any range. In addition, whenever a numerical range is indicated in the present application, it refers to any cited number (fraction or integer) in the indicated range.

[0027] In the description of the present application, the terms "include", "contain" and the like mean "include but not limited to". In the present application, "and / or" describes the association relationship of the associated objects, which means that there can be three kinds of relationships, for example, A and / or B can mean that A exists alone, A and B exist together, and B exists alone. Wherein A and B can be singular or plural. In the present application, "at least one" means one or more, and "multiple" means two or more. "At least one", "at least one of the following" or the like means any combination of the items, including any combination of single item or multiple items. For example, "at least one of a, b or c", or "at least one of a, b and c", can mean a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, wherein a, b and c can be single or multiple.

[0028] The silicon-aluminum composite coated titanium dioxide provided by the present application, a preparation method and applications thereof will be described in detail below.

[0029] The existing titanium dioxide coating method usually adopts a step-by-step process, that is, a silicon layer is first deposited under acidic or weak alkaline conditions, and then an aluminum layer is coated under alkaline conditions. The silicon deposition process is highly sensitive to pH changes, and it is difficult to control, which easily causes uneven thickness or loose structure of the film layer, and the film layer has weak adhesion to the substrate, and is prone to peeling or cracking in the subsequent process, affecting the coating stability. In the aluminum coating stage, the surface charge neutralization easily causes particle agglomeration, resulting in uneven coating, and reducing the dispersibility and optical performance. In the multi-step coating process, the interface between different film layers is poorly bonded, and is prone to delamination or peeling under high temperature or shearing conditions, which limits the stability and weather resistance of the material.

[0030] Based on this, the inventors propose the following technical solutions through a large amount of research and practice.

[0031] Some embodiments of the present application provide a preparation method of silicon-aluminum composite coated titanium dioxide, which comprises: under constant temperature conditions of 60-80°C, simultaneously adding sodium metasilicate solution and aluminum sulfate solution to titanium dioxide slurry with a pH value of 7.0-8.0 for coating reaction, the dropping time is ≥60 min, and the pH value of the reaction system is maintained at 6-8 through a buffer system during the dropping process.

[0032] It should be noted that simultaneous dropping refers to using a constant flow pump to add sodium metasilicate solution and aluminum sulfate solution to the system at the same speed in a synchronous manner. During the reaction process, a buffer system is introduced to stabilize the reaction pH at 6.0-8.0, so as to build a suitable near-neutral environment, slow down the condensation rate of silicates, and effectively inhibit the hydrolysis tendency of aluminum ions, realize the simultaneous deposition of silicon and aluminum components on the surface of titanium dioxide, and form a continuous and dense composite coating layer.

[0033] In some embodiments, referring to Figure 1 , the preparation method of silicon-aluminum composite coated titanium dioxide specifically comprises the following steps: S1, preparing titanium dioxide slurry.

[0034] Specifically, the titanium dioxide is dispersed in deionized water to prepare a stable slurry, and the pH of the system is adjusted to 7-8.

[0035] Illustratively, the pretreated titanium dioxide is slowly added to deionized water, and is dispersed and stirred by a high-speed shearing device for 30-60 min to form a uniform slurry. Then, a diluted sodium hydroxide solution is slowly added at 65-75°C to adjust the pH of the system to 7.0-8.0, and the stirring is continued for 30 minutes to complete the alkalization pretreatment.

[0036] In some embodiments, the concentration of the sodium hydroxide solution used is 10% to 30%, the reaction temperature is preferably 70°C, and the target pH is 7.0, 7.5, or 8.0. The mass concentration of titanium dioxide in the slurry is controlled at 200 g / L to 350 g / L, for example, 200 g / L, 210 g / L, 220 g / L, 230 g / L, 240 g / L, 250 g / L, 260 g / L, 270 g / L, 280 g / L, 290 g / L, 300 g / L, 310 g / L, 320 g / L, 330 g / L, 340 g / L, or 350 g / L, etc., to ensure that the system has moderate viscosity and good rheological properties, and meets the requirements of industrial continuous coating process.

[0037] S2, silicon-aluminum composite coating reaction.

[0038] Under constant temperature conditions of 60°C to 80°C, sodium metasilicate solution and aluminum sulfate solution are simultaneously added dropwise to the titanium dioxide slurry for coating reaction, the dropwise adding time is ≥60 min, and the pH value of the reaction system is maintained at 6 to 8 through a buffer system during the dropwise adding process.

[0039] For reference, the temperature of the coating reaction can be selected as 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 66°C, 67°C, 68°C, 69°C, 70°C, 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C, 79°C, or 80°C, etc., and preferably, the coating reaction is carried out under constant temperature conditions of 65°C to 75°C. During the coating reaction, temperature is a key parameter for regulating reaction kinetics, crystallization behavior, and interface bonding. Too high or too low temperature will break the balance of “uniform coating-dense film formation-interface bonding”, leading to multiple deteriorations of the structure and performance of the coating layer.

[0040] In some embodiments, the dropwise adding time is 60 min to 120 min, for example, 60 min, 65 min, 70 min, 75 min, 80 min, 85 min, 90 min, 95 min, 100 min, 105 min, 110 min, 115 min, or 120 min, etc., and preferably 80 min to 100 min. Too fast dropwise adding speed will lead to uneven coating, i.e., local concentration in the dropwise adding area will suddenly increase, the hydrolysis / condensation reaction rate will exponentially increase, the product will rapidly aggregate and deposit on the surface of nearby TiO2 particles, forming “local thick coating”, and TiO2 particles away from the dropwise adding area cannot form effective coating layer due to insufficient raw material concentration, leading to “exposed defects”.

[0041] In some embodiments, the concentration of the sodium metasilicate solution is 0.2-0.6 mol / L, for example, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L or 0.6 mol / L, and the concentration of the aluminum sulfate solution is 0.2-0.6 mol / L, for example, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L or 0.6 mol / L.

[0042] In some embodiments, the molar ratio of SiO2 to Na2O in the sodium metasilicate solution is (2.5-3.5):1, for example, 3:1. The mass ratio of the sodium metasilicate to the aluminum sulfate, calculated based on SiO2 and Al2O3, is (2-4):1.

[0043] In some embodiments, the buffer system is a citrate-bicarbonate system. The citrate-bicarbonate buffer system is introduced to stabilize the reaction pH at 6.0-8.0, thereby constructing a suitable near-neutral environment, slowing down the polycondensation rate of silicates, and effectively inhibiting the hydrolysis tendency of aluminum ions, realizing the synergistic deposition of silicon and aluminum components on the surface of titanium dioxide, and forming a continuous and dense composite coating layer.

[0044] Specifically, the total mass of citrate and bicarbonate in the buffer system accounts for 2%-4% of the mass of titanium dioxide.

[0045] S3, aging treatment: after the reaction is completed, continue to incubate the reaction under the same temperature condition to perform preliminary aging, and then perform film layer densification treatment.

[0046] Specifically, continue to incubate the reaction under the same temperature condition for 50-70 min, for example, 60 min.

[0047] In some embodiments, the film layer densification treatment is to add a composite organic acid to the reaction system, adjust the pH to 5-5.5 (add inorganic acid or inorganic alkali solution), and continue to age for 50-70 min under the same temperature condition as the coating reaction.

[0048] The organic acid, as a complexing agent, can undergo coordination reaction with residual unstable silicon and aluminum species in the film layer, promote further rearrangement, crosslinking and polymerization, and effectively improve the denseness and structural integrity of the film layer. This step helps to construct a continuous and defect-free film structure, and at the same time, strengthens the interfacial bonding force between the film coating layer and TiO2. In a mild acidic environment, the etching effect on titanium dioxide is avoided, the optical performance of the product is not affected, and the long-term stability of the coating material is improved.

[0049] S4, final slurry treatment.

[0050] Specifically, the slurry after the densification treatment of the film layer is sequentially subjected to washing, neutralization, drying and crushing.

[0051] In some embodiments, the washed slurry is subjected to flash drying at a temperature of 250-270°C for no more than 8 seconds. Compared with conventional hot air drying, flash drying can significantly reduce film layer shrinkage and crack formation. The dried coarse powder is subjected to steam mill shaping treatment to obtain white fine powder with uniform particle size distribution. The finished product has high whiteness and obvious blue phase, and the scanning electron microscope (SEM) image shows that the film layer is dense and continuous, without naked core phase exposure and obvious agglomeration.

[0052] Some embodiments of the present application also provide a silicon-aluminum composite coated titanium dioxide prepared by the method for preparing a silicon-aluminum composite coated titanium dioxide according to any one of the preceding embodiments. The weather resistance test results show that, compared with commercially available silicon-aluminum coated products, the sample obtained by the embodiments of the present application has significantly improved color retention rate after xenon lamp accelerated aging test, showing good weather resistance and industrial application value, and is suitable for use in the fields of coatings, plastics and the like.

[0053] Some embodiments of the present application also provide the use of the silicon-aluminum composite coated titanium dioxide according to the preceding embodiments in a coating or plastic product.

[0054] The features and properties of the present application are further described in detail below in combination with examples.

[0055] Example 1 The present embodiment provides a method for preparing a silicon-aluminum composite coated titanium dioxide, and the specific steps are as follows: (1) The sand-milled rutile titanium dioxide is dispersed in deionized water to prepare a slurry with a concentration of 250 g / L, and stirred and dispersed at room temperature for 30 min.

[0056] (2) The slurry is heated to 70°C, and 10% sodium hydroxide solution is slowly added to adjust the pH to 7.5.

[0057] (3) Sodium metasilicate solution (0.4 mol / L) with a modulus of 3 and aluminum sulfate solution (0.4 mol / L) are simultaneously and constantly added at the same speed, and buffer solution (sodium citrate:sodium bicarbonate mass ratio of 1:1, accounting for 3% of the mass of titanium dioxide) is synchronously added, so as to maintain the pH at 7.0, and the addition is performed for 90 min.

[0058] (4) After the addition is completed, the stirring is continued at 70°C for 60 min, 0.8wt% organic acid (citric acid: lactic acid = 1:3) is added for further reaction for 60 min, and then filtration, water washing, drying and steam milling are performed. The washed slurry is subjected to flash drying at a temperature of 260°C for 6 seconds.

[0059] Example 2 The present example provides a preparation method of silicon-aluminum composite coated titanium dioxide, which is different from example 1 in that the mass of the buffer solution accounts for 2% of the titanium dioxide in step (3).

[0060] Example 3 The present example provides a preparation method of silicon-aluminum composite coated titanium dioxide, which is different from example 1 in that the mass of the buffer solution accounts for 4% of the titanium dioxide in step (3).

[0061] Example 4 The present example provides a preparation method of silicon-aluminum composite coated titanium dioxide, which is different from example 1 in that the ratio of sodium citrate to sodium bicarbonate is 3:1 in step (3), and the pH is maintained at 6 during the dropping process.

[0062] Example 5 The present example provides a preparation method of silicon-aluminum composite coated titanium dioxide, which is different from example 1 in that the ratio of sodium citrate to sodium bicarbonate is 1:3 in step (3), and the pH is maintained at 8 during the dropping process.

[0063] Example 6 The present example provides a preparation method of silicon-aluminum composite coated titanium dioxide, which is different from example 1 in that the temperature is maintained at 60°C during the dropping process in step (3).

[0064] Example 7 The present example provides a preparation method of silicon-aluminum composite coated titanium dioxide, which is different from example 1 in that the temperature is maintained at 80°C during the dropping process in step (3).

[0065] Example 8 The present example provides a preparation method of silicon-aluminum composite coated titanium dioxide, which is different from example 1 in that the aluminum sulfate solution is changed to an aluminum chloride solution in step (3).

[0066] Comparative Example 1 The present comparative example is different from example 1 only in that no buffer solution is added, and the sodium metasilicate solution is added first, followed by the addition of the aluminum sulfate solution.

[0067] Comparative Example 2 The present comparative example is different from example 1 only in that the sodium metasilicate and the aluminum sulfate solution are added quickly and at once within 3 min.

[0068] Comparative Example 3 The present comparative example is different from example 1 only in that no buffer solution is added at all.

[0069] Comparative Example 4 The present comparative example differs from Example 1 only in that the organic acid densification treatment is not performed.

[0070] Comparative Example 5 The present comparative example differs from Example 1 only in that the temperature is maintained at 50°C during the dropwise addition in step (3).

[0071] Comparative Example 6 The present comparative example differs from Example 1 only in that the temperature is maintained at 90°C during the dropwise addition in step (3).

[0072] Comparative Example 7 The present comparative example differs from Example 1 only in that the dropwise addition time is 30 min in step (3).

[0073] Test Example 1 To evaluate the acid solubility and weather resistance of the silicon-aluminum composite-coated titanium dioxide prepared in the examples and comparative examples, the following tests were performed: Acid solubility test: The titanium dioxide sample was dispersed in concentrated sulfuric acid at a certain ratio, transferred to a graphite digester, and heated at 175°C for 1 hour; ice water was quickly added for dilution and cooling, and hydrogen peroxide was introduced into the solution to complex free titanium ions, and then the acid solubility was determined by visible spectrophotometry. The results are shown in Table 1.

[0074] Weather resistance test: The samples of the examples and comparative examples were dispersed in acrylic resin to prepare thin film samples. They were placed in a xenon lamp accelerated aging device and continuously irradiated at 75° for 1500 hours. The color parameter changes of the samples before and after the test were determined using a spectrophotometer, and ΔL * , Δa * , Δb * and ΔE * were recorded. The test results are shown in Table 1.

[0075] Table 1 Acid solubility and weather resistance test results

[0076] Note: The reference sample in Table 1 is a commercially available general-purpose rutile titanium dioxide product used as a performance comparison benchmark.

[0077] Test Example 2 The coated products obtained in Example 1 and Comparative Example 1 were subjected to scanning electron microscope analysis, and the results are shown in Figure 2 and Figure 3 .

[0078] Figure 2 The SEM image of the sample of Comparative Example 1 is Figure 3SEM image of the sample of Example 1. As can be seen from the figure, the surface coating layer of the sample prepared in Example 1 is continuous and dense, the particles are uniformly distributed, and there is substantially no obvious agglomeration; in contrast, there is obvious agglomeration between the particles in the sample of Comparative Example 1, the surface coating is incomplete, and there is a bare titanium dioxide matrix in some areas, indicating that the uniformity and density are insufficient.

[0079] The above comparison results show that, by using sodium metasilicate and aluminum sulfate as the silicon and aluminum sources, and by stabilizing the pH of the coating reaction to between 6 and 8 under the action of the citrate-bicarbonate buffer system, the silicon acid polymerization rate can be effectively slowed down and the tendency of aluminum salt hydrolysis can be inhibited, thereby promoting the synergistic deposition of silicon and aluminum components on the surface of titanium dioxide, and forming a composite coating layer that is dense and stable in structure.

[0080] In addition, the method of the embodiments of the present application is simple and easy to control, and the introduction of the buffer adjustment system not only improves the film formation quality of the coating layer, but also effectively avoids problems such as particle agglomeration and uneven coating, thereby improving the appearance quality of the product and enhancing its weather resistance and stability.

[0081] The above only describes preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing silicon-aluminum composite coated titanium dioxide, characterized in that, It includes: Under constant temperature conditions of 60℃~80℃, sodium metasilicate solution and aluminum sulfate solution were simultaneously added dropwise to titanium dioxide slurry with a pH value of 7.0~8.0 to carry out a coating reaction. The addition time was ≥60min. During the addition process, the pH value of the reaction system was maintained at 6~8 through a buffer system.

2. The preparation method of silicon-aluminum composite coated titanium dioxide according to claim 1, characterized in that, The coating reaction was carried out under constant temperature conditions of 65℃~75℃; And / or, the dripping time is 60 min to 120 min, preferably 80 min to 100 min.

3. The preparation method of silicon-aluminum composite coated titanium dioxide according to claim 1, characterized in that, The concentration of the titanium dioxide slurry is 200 g / L to 350 g / L, the concentration of the sodium metasilicate solution is 0.2 mol / L to 0.6 mol / L, and the concentration of the aluminum sulfate solution is 0.2 mol / L to 0.6 mol / L.

4. The preparation method of silicon-aluminum composite coated titanium dioxide according to claim 3, characterized in that, In the sodium metasilicate solution, the molar ratio of SiO2 to Na2O is (2.5~3.5):1; And / or, based on SiO2 and Al2O3, the mass ratio of sodium metasilicate to aluminum sulfate is (2~4):1.5, and the total mass of sodium metasilicate and aluminum sulfate added is (3.5~5.5):100 to the mass of titanium dioxide.

5. The preparation method of silicon-aluminum composite coated titanium dioxide according to claim 3, characterized in that, The buffer system is a citrate-bicarbonate system; Preferably, the total mass of citrate and bicarbonate in the buffer system accounts for 2% to 4% of the mass of titanium dioxide.

6. The method for preparing silicon-aluminum composite coated titanium dioxide according to any one of claims 1 to 5, characterized in that, The preparation steps of the titanium dioxide slurry include: dispersing titanium dioxide in deionized water to prepare a stable slurry, and adjusting the pH of the system to 7-8; Preferably, a diluted sodium hydroxide solution is slowly added dropwise at a temperature of 65-75°C to adjust the pH of the system to 7.0-8.0, and the mixture is kept warm and stirred for 20-40 minutes. More preferably, the mass concentration of the sodium hydroxide solution is 10%-30%.

7. The method for preparing silicon-aluminum composite coated titanium dioxide according to any one of claims 1 to 5, characterized in that, Also includes: After the sodium metasilicate solution and aluminum sulfate solution are added dropwise, the reaction is continued at the same temperature as the coating reaction for 50 min to 70 min, and the film layer is densified. Preferably, the membrane densification treatment involves adding a composite organic acid, adjusting the pH to 5-5.5, and aging for 50-70 minutes at the same temperature as the coating reaction.

8. The method for preparing silicon-aluminum composite coated titanium dioxide according to claim 7, characterized in that, It also includes sequentially washing, neutralizing, drying, and pulverizing the slurry that has undergone membrane densification treatment; Preferably, the washed slurry is flash-dried at a temperature of 250~270℃ for a drying time not exceeding 8 seconds.

9. A silicon-aluminum composite coated titanium dioxide, characterized in that, It is prepared by the method for preparing silicon-aluminum composite coated titanium dioxide as described in any one of claims 1 to 8.

10. The application of the silicon-aluminum composite coated titanium dioxide as described in claim 9 in coatings or plastic products.

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