High-whiteness and yellowing-resistant rutile titanium dioxide, and preparation method and application thereof

Abstract

This invention discloses a high-whiteness, yellowing-resistant rutile titanium dioxide, its preparation method, and its applications, belonging to the technical field of titanium dioxide preparation and high-end coating applications. The titanium dioxide uses rutile titanium dioxide as a base material, with a gradient inorganic composite coating layer and a stepwise organic composite coating layer sequentially coated on its surface. The inorganic coating is a three-layer structure consisting of a silicon-zinc composite dense layer, a zirconium compound barrier layer, and an aluminum compound buffer dispersion layer. The organic coating is a two-layer structure consisting of an anchoring compatibility layer of silane coupling agent and polyether polyol, and a functional lubricating layer of hindered amine light stabilizer and pentaerythritol stearate. This invention solves the industry pain point of difficulty in simultaneously achieving good weather resistance and yellowing resistance while maintaining whiteness, gloss, and dispersibility through the synergistic effect of the inorganic-organic coating. The preparation process is stable and controllable, easily scaled up industrially, and the product can be widely used in various high-end coating systems.

Description

Technical Field

[0001] This invention belongs to the technical field of titanium dioxide preparation and high-end coating application. Specifically, it relates to a high-whiteness, yellowing-resistant rutile titanium dioxide, its preparation method and application, which is particularly suitable for coating systems with stringent requirements for pigment whiteness, yellowing resistance, gloss, weather resistance and dispersibility, such as high weather-resistant exterior wall coatings, water-based industrial coatings, automotive repair paints, and high-end plastic paints. Background Technology

[0002] Rutile titanium dioxide (titanium dioxide) is currently the world's best-performing white pigment. With its extremely high refractive index, excellent hiding power, whiteness, and chemical stability, it is widely used in coatings, plastics, inks, and papermaking. The coatings industry accounts for over 60% of total titanium dioxide consumption, making it the largest application area. In coating systems, the performance of titanium dioxide directly determines core indicators such as whiteness, sharpness, gloss, weather resistance, and storage stability of the paint film. This is especially true for high-end exterior wall coatings, water-based industrial coatings, and automotive coatings, which place extremely high demands on the comprehensive performance of titanium dioxide.

[0003] However, unmodified rutile titanium dioxide has inherent defects: First, the surface of titanium dioxide has a large number of photoactive sites, which will produce a photocatalytic effect under ultraviolet light irradiation, decomposing the film-forming substances in the paint film, leading to aging phenomena such as chalking, loss of gloss, and yellowing, and seriously shortening the service life of the coating. Second, titanium dioxide has a small original particle size and high surface energy, making it very easy to agglomerate. Its poor dispersibility in the coating system will not only reduce the hiding power, whiteness and gloss of the paint film, but also cause problems such as sedimentation and coarsening during the storage of the coating. Third, titanium dioxide has a high hydroxyl content on its surface, which has poor compatibility with water-based / oil-based coating film-forming systems, making it prone to interface defects and reducing the density and corrosion resistance of the paint film.

[0004] To address the aforementioned issues, the industry employs inorganic-organic coating modification technology for titanium dioxide surface treatment. Existing technologies often utilize single silica-alumina or zirconium-alumina coatings, which only achieve basic improvements in weather resistance or dispersibility, exhibiting significant technical shortcomings: single silica-alumina coatings lack sufficient density to completely seal the photoactive sites of titanium dioxide, leading to yellowing and chalking with long-term use; single zirconium-alumina coatings are costly and offer limited improvement in whiteness and dispersibility, failing to meet the high-gloss requirements of high-end coatings. Meanwhile, existing organic coatings often employ single silane coupling agents, stearic acid, or titanate coupling agents, improving only the dispersibility of a single system and failing to simultaneously address compatibility with both water-based and oil-based coating systems. Furthermore, the bonding between the organic coating and the inorganic coating layer is primarily physical adsorption, resulting in weak adhesion and easy coating detachment during coating processing, thus failing to achieve a synergistic improvement in weather resistance and dispersibility.

[0005] In addition, existing technologies generally suffer from a technical contradiction of "performance seesaw": improving the weather resistance and yellowing resistance of titanium dioxide often leads to a decrease in whiteness, gloss and dispersibility; while improving dispersibility and gloss sacrifices weather resistance and long-term stability, making it impossible to achieve the synergistic effect of multiple properties such as high whiteness, yellowing resistance, high gloss, high weather resistance and high dispersibility at the same time.

[0006] Therefore, developing a rutile titanium dioxide that can simultaneously achieve high whiteness, excellent resistance to yellowing, high gloss, high weather resistance, and wide system dispersibility through the synergistic effect of inorganic-organic coatings, and solving the performance shortcomings of existing technologies, is of great practical significance and economic value for promoting the upgrading of the domestic titanium dioxide industry, replacing imported products, and expanding the high-end coating application market. Summary of the Invention

[0007] To address the shortcomings of existing titanium dioxide technologies that cannot simultaneously achieve high whiteness, resistance to yellowing, high gloss, high weather resistance, and excellent dispersibility, this invention aims to provide a high-whiteness, yellowing-resistant rutile titanium dioxide. Through a structural design combining gradient inorganic composite coating and stepwise organic composite coating, a synergistic effect of the inorganic-organic coating is achieved, simultaneously solving the core problems of photocatalytic yellowing, poor dispersibility, and insufficient compatibility with coating systems. Another objective of this invention is to provide a preparation method for this titanium dioxide, with a stable and controllable process that is easy to scale up industrially. A further objective is to provide applications of this titanium dioxide in high-end coatings, significantly improving the overall performance of coating films and expanding the application scope of domestically produced titanium dioxide.

[0008] The objective of this invention can be achieved through the following technical solutions: A high-whiteness, yellowing-resistant rutile titanium dioxide comprises a rutile titanium dioxide substrate, an inorganic composite coating layer covering the surface of the substrate, and an organic composite coating layer covering the outer surface of the inorganic composite coating layer. Based on 100 parts by weight of the rutile titanium dioxide substrate, the inorganic composite coating layer comprises the following components in parts by weight: 2-6 parts of silicon compound coating component, 1-4 parts of zinc compound coating component, 3-8 parts of zirconium compound coating component, and 5-12 parts of aluminum compound coating component. The organic composite coating layer comprises the following components in parts by weight: 0.5-2 parts of silane coupling agent, 0.3-1.5 parts of polyether polyol, 0.2-1 part of hindered amine light stabilizer, and 0.1-0.8 parts of pentaerythritol stearate.

[0009] Furthermore, the rutile titanium dioxide substrate is a primary rutile titanium dioxide product prepared by the sulfuric acid method or the chloride method, with a primary particle size of 0.2-0.35μm and a rutile crystal content of ≥98.5%. Titanium dioxide in this particle size range has the best whiteness, hiding power and gloss, which is suitable for the application requirements of high-end coatings.

[0010] Furthermore, the inorganic composite coating layer consists of a first inorganic coating layer, a second inorganic coating layer, and a third inorganic coating layer, arranged sequentially from the substrate outwards. The first inorganic coating layer is a dense composite layer of silicon and zinc compounds, the second inorganic coating layer is a zirconium compound barrier layer, and the third inorganic coating layer is an aluminum compound buffer and dispersion layer. This three-layer gradient coating structure design achieves a functional progression from "photoactive sealing - dielectric barrier - dispersion and buffering," with synergistic effects between each layer, far exceeding the performance of traditional single inorganic coatings.

[0011] Further, the silicon compound is at least one of sodium silicate, tetraethyl orthosilicate, and fumed silica; the zinc compound is at least one of zinc sulfate, zinc nitrate, and zinc oxide; the zirconium compound is at least one of zirconium oxychloride, zirconium sulfate, and zirconium nitrate; and the aluminum compound is at least one of sodium aluminate, aluminum sulfate, and aluminum nitrate.

[0012] Further, the silane coupling agent is at least one of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, and vinyltriethoxysilane; the polyether polyol is at least one of polypropylene glycol and polytetrahydrofuran ether glycol with a number average molecular weight of 2000-6000; and the hindered amine light stabilizer is at least one of light stabilizer 944, light stabilizer 622, and light stabilizer 770.

[0013] Furthermore, the organic composite coating layer consists of a first organic coating layer and a second organic coating layer, arranged sequentially from the inorganic composite coating layer outwards. The first organic coating layer is an anchoring and compatibility layer of silane coupling agent and polyether polyol, while the second organic coating layer is a functional lubricating layer of hindered amine light stabilizer and pentaerythritol stearate. This stepwise organic coating structure achieves a progressive effect from "interface anchoring - system compatibility - functional enhancement," forming chemical bonds with the inorganic coating layer rather than simple physical adsorption, resulting in stronger coating adhesion and more stable performance.

[0014] This invention also provides a method for preparing the above-mentioned high-whiteness, yellowing-resistant rutile titanium dioxide, comprising the following steps: S1. Slurry preparation: Mix rutile titanium dioxide substrate with deionized water, add dispersant for high-speed dispersion, adjust the pH value of the slurry, and obtain a uniform titanium dioxide slurry. S2. Inorganic composite coating: The titanium dioxide slurry obtained in S1 is heated to a set temperature, and the first inorganic coating, the second inorganic coating, and the third inorganic coating are carried out in sequence. After each coating step is completed, constant temperature curing is performed to obtain inorganic coated titanium dioxide slurry. S3. Washing and drying: The inorganic coated titanium dioxide slurry obtained in S2 is washed and filtered by pressure. The filter cake is dried and pulverized to obtain inorganic coated titanium dioxide powder. S4. Organic composite coating: The inorganic coated titanium dioxide powder obtained in S3 is added to a high-speed mixer. After the temperature is increased by program, the first organic coating and the second organic coating are carried out in sequence. After each coating step is completed, constant temperature curing is carried out to obtain the organic coated powder. S5. Airflow milling: The organic-coated powder obtained in S4 is subjected to ultra-fine airflow milling to obtain the high-whiteness, yellowing-resistant rutile titanium dioxide.

[0015] Further, in step S1, the solid content of the titanium dioxide slurry is 300-400 g / L, the dispersant is sodium hexametaphosphate, and the amount added is 0.1-0.3% of the mass of the rutile titanium dioxide substrate. The high-speed dispersion time is 20-40 min. The pH value of the slurry is adjusted to 9.0-10.0 using a 10% sodium hydroxide solution or sulfuric acid solution. The alkaline environment can ensure that the titanium dioxide powder is fully dispersed and avoids agglomeration, laying the foundation for subsequent uniform coating.

[0016] Furthermore, the specific operation of step S2 is as follows: S21. First Inorganic Coating: The titanium dioxide slurry is heated to 60-80℃, and a mixed aqueous solution of silicon and zinc compounds is added at a uniform rate. At the same time, the pH value of the system is adjusted to 8.0-9.5 using a 10% sulfuric acid solution. The feeding time is 60-120 minutes, and after the feeding is completed, it is kept at a constant temperature for 30-60 minutes. Under these pH and temperature conditions, the silicon and zinc compounds can be hydrolyzed and deposited simultaneously on the surface of the titanium dioxide to form a uniform and dense amorphous silicon oxide-zinc oxide composite film, which completely adheres to the surface of the titanium dioxide substrate, deeply seals the photoactive sites, and inhibits the photocatalytic reaction from the source. At the same time, zinc oxide can absorb ultraviolet light, further improving the yellowing resistance. S22. Second inorganic coating: Add zirconium compound aqueous solution to the slurry after S21 curing at a uniform rate, while adjusting the pH of the system to 4.0-5.5 with 10% sodium hydroxide solution. The addition time is 40-90 min, and after the addition is completed, cure at a constant temperature for 20-40 min. Under these acidic conditions, the zirconium oxide film formed by the hydrolysis of zirconium compound has extremely high density and hardness. It can form a dense barrier layer outside the silicon-zinc composite layer, effectively preventing water, oxygen and corrosive media from penetrating into the titanium dioxide substrate, greatly improving the weather resistance of the coating film. At the same time, the strong adhesion between zirconium oxide and the inner and outer layers of the film can prevent the coating layer from falling off. S23. Third Inorganic Coating: Add an aqueous solution of aluminum compound to the slurry after S22 curing at a uniform rate, while adjusting the pH of the system to 6.5-7.5 with a 10% sulfuric acid solution or sodium hydroxide solution. The feeding time is 50-100 min, and after the feeding is completed, cure at a constant temperature for 40-80 min. Under these neutral conditions, the aluminum compound hydrolyzes to form a loose boehmite-type alumina film, which can form a buffer layer on the outermost layer, reduce the surface energy of the powder, prevent powder agglomeration, and significantly improve the dispersibility of titanium dioxide. At the same time, alumina can neutralize acidic substances in the system, improve the storage stability of titanium dioxide, and further optimize whiteness and gloss.

[0017] Further, in step S3, the slurry is countercurrently washed with deionized water until the conductivity of the washing filtrate is ≤50μS / cm to remove soluble salt impurities and avoid impurities affecting the whiteness and yellowing resistance of titanium dioxide; the filter cake after pressure filtration is dried with hot air at 120-150℃ for 10-15h, and after drying, it is coarsely pulverized with a universal pulverizer to obtain inorganic coated titanium dioxide powder.

[0018] Furthermore, the specific operation of step S4 is as follows: S41. First Organic Coating: Inorganic coated titanium dioxide powder is added to a high-speed mixer and heated to 80-100℃. A mixture of silane coupling agent and polyether polyol preheated to 60℃ is added at a uniform rate. The mixture is then mixed at a high speed of 1500-2000 r / min for 15-30 min to complete the first organic coating. At this temperature, the alkoxy groups of the silane coupling agent can undergo a dehydration condensation reaction with the hydroxyl groups on the surface of the inorganic coating layer to form stable Si-O-Si covalent bonds, firmly anchoring the organic molecules to the surface of the inorganic coating layer and preventing the coating from falling off. At the same time, the hydroxyl groups of the polyether polyol can react with the active groups of the silane coupling agent to introduce a large number of flexible ether bonds on the powder surface, which greatly improves the compatibility and dispersion stability of titanium dioxide in water-based acrylic, polyurethane and other coating film-forming systems. S42. Second Organic Coating: Continue heating the system to 100-120℃, add the pre-molten hindered amine light stabilizer and pentaerythritol stearate mixture, mix at high speed at 1500-2000 r / min for 20-40 min, and cure at a constant temperature for 10-20 min to complete the second organic coating; at this temperature, the hindered amine light stabilizer can be uniformly coated on the powder surface, and by capturing free radicals generated by ultraviolet light irradiation, it blocks the photoaging chain reaction, forming a triple weather-resistant and yellowing-resistant protection system with the photoactive sealing and ultraviolet blocking of the inorganic coating layer; pentaerythritol stearate can form a lubricating layer on the powder surface, reduce the friction between powders, improve the flowability of titanium dioxide and its dispersibility in oil-based coating systems, and at the same time optimize the leveling properties of the paint film, significantly improving the gloss and sharpness of the paint film.

[0019] Furthermore, in step S5, a flat air jet mill is used for ultrafine grinding, with a grinding pressure of 0.6-1.0 MPa and a classifying wheel speed of 3000-5000 r / min. The powder is dispersed by air jet milling, and the uniformity of the organic coating is further optimized to obtain a finished titanium dioxide with uniform particle size distribution and excellent dispersibility.

[0020] This invention also provides the application of the above-mentioned high-whiteness, yellowing-resistant rutile titanium dioxide in the field of high-end coatings, including high-weather-resistant water-based exterior wall coatings, water-based industrial anti-corrosion coatings, automotive refinish paints, high-end plastic paints, wood coatings, etc. Adding the titanium dioxide of this invention as a white pigment to the coating system at an addition amount of 10-30% of the total mass of the coating can significantly improve the whiteness, gloss, yellowing resistance, weather resistance, and storage stability of the coating film.

[0021] The beneficial effects of this invention are: (1) This invention designs a three-layer gradient inorganic coating structure of “silicon-zinc dense layer - zirconium barrier layer - aluminum dispersion layer”, breaking through the performance bottleneck of traditional single coating. The inner silicon-zinc composite film can completely seal the photoactive sites of titanium dioxide, inhibiting yellowing and chalking caused by photocatalysis from the root. The ultraviolet absorption characteristics of zinc oxide and the dense barrier of silicon oxide form a synergy. The middle zirconium layer forms a highly dense barrier to prevent the penetration of water, oxygen and corrosive media. The outer aluminum layer optimizes dispersibility and whiteness, realizing the functional progression of “sealing-barrier-dispersion”. The synergistic effect of the quaternary inorganic components effectively improves the yellowing resistance of titanium dioxide compared with traditional silicon-aluminum coating, solving the long-standing industry pain point of easy yellowing and chalking of titanium dioxide when used outdoors.

[0022] (2) This invention designs a two-step organic coating structure of "anchoring compatibility layer - functional lubrication layer", which overcomes the shortcomings of traditional organic coatings, such as weak bonding force and limited compatibility with a single system. The inner silane coupling agent forms a covalent bond with the inorganic coating layer, and the coating bonding force is better than physical adsorption, preventing the coating from falling off during coating processing. The flexible ether bonds introduced by the polyether polyol greatly improve the compatibility and storage stability of titanium dioxide in water-based coating systems. The outer hindered amine light stabilizer forms a triple weather-resistant protection with the inorganic coating, and pentaerythritol stearate optimizes the dispersibility and film leveling properties of oil-based systems. The synergistic effect of the quaternary organic components achieves a wide range of compatibility with water-based / oil-based coating systems, effectively improves dispersion stability, and further enhances resistance to yellowing and weathering.

[0023] (3) The core inventiveness of this invention lies in achieving a deep synergistic effect between inorganic and organic composite coatings: the inorganic coating layer not only provides basic whiteness, yellowing resistance, and weather resistance, but its abundant hydroxyl groups provide a large number of reactive sites for the organic coating, ensuring uniform and firm coating; the organic coating layer not only solves the problems of easy agglomeration and poor dispersibility of inorganic coating powder, but its free radical capture function synergizes with the photoactive blocking and ultraviolet blocking of the inorganic coating, further improving weather resistance and yellowing resistance. At the same time, by optimizing the interfacial compatibility between titanium dioxide and the coating system, the gloss and vividness of the paint film are greatly improved. The synergistic effect of the two completely solves the technical contradiction in the prior art that "improving weather resistance reduces whiteness and gloss, and improving dispersibility sacrifices weather resistance", and at the same time achieves multiple performance synergies of high whiteness, excellent yellowing resistance, high gloss, high weather resistance, and excellent dispersibility.

[0024] (4) The preparation method of the present invention ensures the uniformity, density and firmness of each coating layer by precisely controlling the pH value, temperature, feeding time and curing time of each coating step, avoiding problems such as uneven coating, local agglomeration and film peeling; the process does not involve high temperature and high pressure operation, does not use toxic and harmful reagents, is green and environmentally friendly, has low equipment requirements, is highly compatible with existing titanium dioxide industrial production lines, can achieve mass production without large-scale equipment modification, and has controllable production costs, making it suitable for large-scale industrial promotion. Detailed Implementation

[0025] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the following detailed description of the specific implementation methods, structures, features and effects of the present invention, in conjunction with embodiments, is provided below.

[0026] In the following examples and comparative examples, all raw materials used are industrial-grade qualified products that can be purchased through commercial channels; the rutile titanium dioxide substrate used is a primary rutile titanium dioxide product prepared by the chloride process, with a native particle size of 0.25 μm and a rutile crystal content of 99.0%. Based on 100 parts by mass of this substrate, all coating components are measured in parts by mass.

[0027] Example 1 This embodiment is the optimal embodiment of the present invention. The formulation of high whiteness and yellowing-resistant rutile titanium dioxide is as follows: Based on 100 parts by weight of rutile titanium dioxide substrate, the inorganic composite coating layer consists of: 4 parts sodium silicate, 2 parts zinc sulfate, 5 parts zirconium oxychloride, and 8 parts sodium aluminate; the organic composite coating layer consists of: 1 part γ-aminopropyltriethoxysilane, 0.8 parts polypropylene glycol (number average molecular weight 4000), 0.5 parts light stabilizer 944, and 0.4 parts pentaerythritol stearate.

[0028] The specific steps of the preparation method are as follows: S1. Slurry preparation: Mix 100 parts by weight of rutile titanium dioxide substrate with deionized water, add 0.2 parts by weight of sodium hexametaphosphate dispersant, disperse at high speed for 30 minutes, and prepare a uniform slurry with a solid content of 350 g / L. Adjust the pH value of the slurry to 9.5 with 10% sodium hydroxide solution and set aside. S2. Inorganic composite coating: S21. First inorganic coating: The slurry obtained in S1 is heated to 70°C, and a mixed aqueous solution of sodium silicate and zinc sulfate (containing 4 parts sodium silicate, 2 parts zinc sulfate, and 50 parts deionized water) is added at a uniform rate. At the same time, the pH value of the system is adjusted to be stable at 9.0 using a 10% sulfuric acid solution. The feeding time is 90 min, and after the feeding is completed, it is kept at a constant temperature for 45 min. S22. Second inorganic coating: Add zirconium oxychloride aqueous solution (containing 5 parts zirconium oxychloride and 30 parts deionized water) to the slurry after S21 curing at a uniform rate, while adjusting the pH value of the system to stabilize at 5.0 with 10% sodium hydroxide solution. The feeding time is 60 min, and after the feeding is completed, the slurry is cured at a constant temperature for 30 min. S23. Third inorganic coating: Add sodium aluminate aqueous solution (containing 8 parts sodium aluminate and 40 parts deionized water) to the slurry after S22 curing at a uniform rate, while adjusting the pH value of the system to be stable at 7.0 with 10% sulfuric acid solution. The feeding time is 75 min, and after the feeding is completed, the slurry is cured at a constant temperature for 60 min to obtain inorganic coated titanium dioxide slurry. S3. Washing and drying: The slurry obtained in S2 is washed countercurrently with deionized water until the conductivity of the washing filtrate is ≤50μS / cm. After washing, the slurry is filtered by pressure. The filter cake is placed in a hot air drying oven and dried at 120℃ for 12 hours. After drying, it is coarsely pulverized by a universal pulverizer to obtain inorganic coated titanium dioxide powder. S4. Organic composite coating: S41. First organic coating: Add the inorganic coated titanium dioxide powder obtained in S3 to a high-speed mixer, heat it to 90°C, and add the mixture of γ-aminopropyltriethoxysilane and polyoxypropylene glycol preheated to 60°C at a uniform speed. Mix at high speed at 1800 r / min for 20 min to complete the first organic coating. S42. Second organic coating: The high-speed mixer system is heated to 110°C, and a mixture of pre-melted light stabilizer 944 and pentaerythritol stearate is added. The mixture is then mixed at 1800 r / min for 30 min and cured at a constant temperature for 15 min to complete the second organic coating and obtain the coated powder. S5. Airflow milling: The coated powder obtained in S4 is added to a flat airflow mill, the milling pressure is set to 0.8 MPa, the classifier speed is 4000 r / min, and ultra-fine airflow milling is performed to obtain the high whiteness and yellowing resistant rutile titanium dioxide of this embodiment.

[0029] Example 2 The formulation of high-whiteness, yellowing-resistant rutile titanium dioxide in this embodiment is as follows: Based on 100 parts by weight of rutile titanium dioxide substrate, the inorganic composite coating layer consists of: 2 parts sodium silicate, 1 part zinc sulfate, 3 parts zirconium oxychloride, and 5 parts sodium aluminate; the organic composite coating layer consists of: 0.5 parts γ-glycidyl etheroxypropyltrimethoxysilane, 0.3 parts polytetrahydrofuran ether diol (number average molecular weight 2000), 0.2 parts light stabilizer 622, and 0.1 parts pentaerythritol stearate.

[0030] The specific steps of the preparation method are as follows: S1. Slurry preparation: Mix 100 parts by weight of rutile titanium dioxide substrate with deionized water, add 0.1 parts by weight of sodium hexametaphosphate dispersant, disperse at high speed for 20 minutes, and prepare a uniform slurry with a solid content of 300 g / L. Adjust the pH value of the slurry to 9.0 with 10% sodium hydroxide solution and set aside. S2. Inorganic composite coating: S21. First inorganic coating: The slurry obtained in S1 is heated to 60°C, and a mixed aqueous solution of sodium silicate and zinc sulfate (containing 2 parts sodium silicate, 1 part zinc sulfate and 30 parts deionized water) is added at a uniform rate. At the same time, the pH value of the system is adjusted to stabilize at 8.0 using 10% sulfuric acid solution. The feeding time is 60 min, and after the feeding is completed, it is kept at a constant temperature for 30 min. S22. Second inorganic coating: Add zirconium oxychloride aqueous solution (containing 3 parts zirconium oxychloride and 20 parts deionized water) to the slurry after S21 curing at a uniform rate, while adjusting the pH value of the system to stabilize at 4.0 with 10% sodium hydroxide solution. The feeding time is 40 min, and after the feeding is completed, the slurry is cured at a constant temperature for 20 min. S23. Third inorganic coating: Add sodium aluminate aqueous solution (containing 5 parts sodium aluminate and 30 parts deionized water) to the slurry after S22 curing at a uniform rate. At the same time, use 10% sulfuric acid solution to adjust the pH value of the system to stabilize at 6.5. The feeding time is 50 min. After the feeding is completed, keep the temperature constant for 40 min to obtain inorganic coated titanium dioxide slurry. S3. Washing and drying: Same as in Example 1; S4. Organic composite coating: S41. First organic coating: Add the inorganic coated titanium dioxide powder to a high-speed mixer, heat it to 80°C, and add the mixture of γ-glycidyl etheroxypropyltrimethoxysilane and polytetrahydrofuran ether diol preheated to 60°C at a uniform speed. Mix at high speed for 15 minutes at 1500 r / min to complete the first organic coating. S42. Second organic coating: The system is heated to 100°C, and a mixture of pre-melted light stabilizer 622 and pentaerythritol stearate is added. The mixture is mixed at 1500 r / min for 20 min and then cured at a constant temperature for 10 min to complete the second organic coating. S5. Airflow milling: Set the milling pressure to 0.6 MPa and the classifier speed to 3000 r / min, and the rest is the same as in Example 1, to obtain the high whiteness and yellowing resistant rutile titanium dioxide of this example.

[0031] Example 3 The formulation of high-whiteness, yellowing-resistant rutile titanium dioxide in this embodiment is as follows: Based on 100 parts by weight of rutile titanium dioxide substrate, the inorganic composite coating layer consists of: 6 parts sodium silicate, 4 parts zinc sulfate, 8 parts zirconium oxychloride, and 12 parts sodium aluminate; the organic composite coating layer consists of: 2 parts γ-methacryloyloxypropyltrimethoxysilane, 1.5 parts polyoxypropylene glycol (number average molecular weight 6000), 1 part light stabilizer 770, and 0.8 parts pentaerythritol stearate.

[0032] The specific steps of the preparation method are as follows: S1. Slurry preparation: Mix 100 parts by weight of rutile titanium dioxide substrate with deionized water, add 0.3 parts by weight of sodium hexametaphosphate dispersant, disperse at high speed for 40 min, and prepare a uniform slurry with a solid content of 400 g / L. Adjust the pH value of the slurry to 10.0 with 10% sodium hydroxide solution and set aside. S2. Inorganic composite coating: S21. First inorganic coating: The slurry obtained in S1 is heated to 80℃, and a mixed aqueous solution of sodium silicate and zinc sulfate (containing 6 parts sodium silicate, 4 parts zinc sulfate and 60 parts deionized water) is added at a uniform rate. At the same time, the pH value of the system is adjusted to be stable at 9.5 using 10% sulfuric acid solution. The feeding time is 120 min, and after the feeding is completed, it is kept at a constant temperature for 60 min. S22. Second inorganic coating: Add zirconium oxychloride aqueous solution (containing 8 parts zirconium oxychloride and 40 parts deionized water) to the slurry after S21 curing at a uniform rate, while adjusting the pH value of the system to stabilize at 5.5 with 10% sodium hydroxide solution. The feeding time is 90 min, and after the feeding is completed, the slurry is cured at a constant temperature for 40 min. S23. Third inorganic coating: Add sodium aluminate aqueous solution (containing 12 parts sodium aluminate and 50 parts deionized water) to the slurry after S22 curing at a uniform rate. At the same time, use 10% sulfuric acid solution to adjust the pH value of the system to stabilize at 7.5. The feeding time is 100 min. After the feeding is completed, the slurry is cured at a constant temperature for 80 min to obtain inorganic coated titanium dioxide slurry. S3. Washing and drying: Same as in Example 1; S4. Organic composite coating: S41. First organic coating: Add the inorganic coated titanium dioxide powder to a high-speed mixer, heat it to 100°C, and add the mixture of γ-methacryloyloxypropyltrimethoxysilane and polyoxypropylene glycol preheated to 60°C at a uniform speed. Mix at high speed at 2000 r / min for 30 min to complete the first organic coating. S42. Second organic coating: The system is heated to 120°C, and a mixture of pre-melted light stabilizer 770 and pentaerythritol stearate is added. The mixture is mixed at 2000 r / min for 40 min and then cured at a constant temperature for 20 min to complete the second organic coating. S5. Airflow milling: Set the milling pressure to 1.0 MPa and the classifier speed to 5000 r / min, and the rest is the same as in Example 1, to obtain the high whiteness and yellowing resistant rutile titanium dioxide of this example.

[0033] Comparative Example 1 The blank control group did not undergo any inorganic or organic coating; the rutile titanium dioxide substrate was directly subjected to air jet milling with the same milling parameters as in Example 1. Comparative Example 2 Only inorganic composite coating is performed, without organic composite coating. The inorganic coating formula and process are the same as in Example 1. After drying and coarse grinding, air jet milling is performed directly. Comparative Example 3 Only organic composite coating is performed, without inorganic composite coating, and the titanium dioxide substrate is directly subjected to the S4 organic coating and S5 air jet milling steps of Example 1; Comparative Example 4 The sodium silicate component was removed from the inorganic composite coating, while the remaining inorganic coating components, dosages, processes, and organic coating were all the same as in Example 1. Comparative Example 5 The zinc sulfate component was removed from the inorganic composite coating, while the remaining inorganic coating components, dosages, processes, and organic coating were all the same as in Example 1. Comparative Example 6 The zirconium oxychloride component was removed from the inorganic composite coating, while the remaining inorganic coating components, dosages, processes, and organic coating were all the same as in Example 1. Comparative Example 7 The sodium aluminate component was removed from the inorganic composite coating, while the remaining inorganic coating components, dosages, processes, and organic coating were all the same as in Example 1. Comparative Example 8 The γ-aminopropyltriethoxysilane component was removed from the organic composite coating, while the remaining organic coating components, dosages, processes, and inorganic coatings were all the same as in Example 1. Comparative Example 9 The polyoxypropylene glycol component was removed from the organic composite coating, while the remaining organic coating components, dosages, processes, and inorganic coating were all the same as in Example 1. Comparative Example 10: The light stabilizer 944 component was removed from the organic composite coating, and the remaining organic coating components, dosages, processes, and inorganic coatings were all the same as in Example 1; Comparative Example 11 The pentaerythritol stearate component was removed from the organic composite coating, while the remaining organic coating components, dosages, processes, and inorganic coatings were all the same as in Example 1. Comparative Example 12 The inorganic composite coating sequence was adjusted to sodium aluminate-zirconium oxychloride-sodium silicate+zinc sulfate, that is, aluminum was coated first, then zirconium was coated, and finally zinc silicate was coated. The pH, temperature, feeding time and curing time of each coating step were the same as in Example 1, and all other steps were the same as in Example 1. Comparative Example 13 The organic composite coating sequence was adjusted to light stabilizer 944 + pentaerythritol stearate-γ-aminopropyltriethoxysilane + polyoxypropylene glycol, that is, the second organic layer was coated first, and then the first organic layer was coated. The temperature, mixing time and curing time of each coating step were the same as in Example 1, and all other steps were the same as in Example 1.

[0034] Performance testing 1. Whiteness (R457) test: According to GB / T 5950-2008 "Method for measuring whiteness of building materials and non-metallic mineral products", an intelligent whiteness meter was used for testing. The titanium dioxide sample was pressed into a flat and uniform test piece. Each sample was tested 3 times and the arithmetic mean was taken. 2. Yellowing Resistance Test: The test was conducted according to GB / T 23983-2009 "Test Method for Yellowing Resistance of Wood Coatings". First, a standard water-based white paint was prepared from a titanium dioxide sample. The formula was: 25 parts by weight of titanium dioxide, 50 parts by weight of water-based acrylic emulsion, 2 parts by weight of alcohol ester film-forming aid, 0.5 parts by weight of sodium polyacrylate dispersant, 0.3 parts by weight of silicone defoamer, 0.2 parts by weight of polyurethane thickener, and 22 parts by weight of deionized water. The white paint was sprayed onto a tinplate to prepare a test panel with a dry film thickness of 50±5μm. After drying at room temperature for 7 days, the panel was placed in an ultraviolet aging test chamber using a UVB-313 lamp with an irradiance of 0.71W / m² and a test temperature of 60℃. After aging for 1000 hours, the color difference value ΔE before and after aging was measured using a colorimeter. The smaller the ΔE, the better the yellowing resistance. 3.60° Gloss Test: According to GB / T 9754-2007 "Determination of 20°, 60° and 85° Specular Gloss of Paint Films without Metallic Pigments", the standard test plate of the above yellowing resistance test was used, and the 60° gloss meter was used for testing. Each sample was tested 3 times and the arithmetic mean was taken. 4. Weather resistance test: The test shall be conducted in accordance with GB / T 1865-2009 "Artificial weathering and artificial radiation exposure (filtered xenon arc radiation) of paints and varnishes". The above standard test plates shall be placed in a xenon lamp aging test chamber with an irradiance of 0.51W / m²@340nm, a black panel temperature of 65℃, a relative humidity of 50%, and a spraying cycle of 18min spraying / 102min drying. After aging for 2000h, the chalking level of the paint film shall be evaluated in accordance with GB / T 1766-2008 "Rating method for aging of paint and varnish coatings". Level 0 is no chalking and level 5 is severe chalking. The lower the level value, the better the weather resistance. 5. Dispersibility test: The test shall be conducted in accordance with GB / T 1724-1979 "Determination of Fineness of Coatings". The titanium dioxide sample shall be added to the water-based acrylic emulsion to prepare a pigment paste with a pigment content of 60%. After dispersing the paste for 30 minutes at 2000 r / min using a high-speed disperser, the fineness of the pigment paste shall be tested using a scraper fineness meter. The unit is μm. The smaller the fineness value, the better the dispersibility. 6. Oil absorption test: Performed in accordance with GB / T 5211.15-2014 "General Test Methods for Pigments and Extenders - Part 15: Determination of Oil Absorption", using linseed oil titration method, with units of g / 100g; 7. pH value test of aqueous suspension: The pH value test shall be performed in accordance with GB / T 1717-1986 "Determination of pH value of pigment aqueous suspension". A 10% (w / w) titanium dioxide aqueous suspension shall be prepared and tested using a precision pH meter.

[0035] Performance test results Table 1 Performance test results of the examples and comparative examples Example 1 95.2 0.8 93.5 Level 0 12 18.5 7.2 Example 2 94.8 0.9 92.8 Level 0 14 19.2 7.0 Example 3 95.5 0.7 94.2 Level 0 13 18.2 7.3 Comparative Example 1 93.0 5.6 80.2 Level 4 35 22.5 6.8 Comparative Example 2 94.5 1.5 85.6 Level 1 25 20.8 7.1 Comparative Example 3 93.2 4.8 83.5 Level 3 22 21.2 6.9 Comparative Example 4 94.0 2.8 88.2 Level 2 18 19.8 7.0 Comparative Example 5 94.2 2.5 89.0 Level 2 17 19.5 7.1 Comparative Example 6 94.3 2.2 89.5 Level 1 16 19.2 7.2 Comparative Example 7 94.1 2.0 87.8 Level 1 28 20.5 7.1 Comparative Example 8 94.8 1.2 90.2 Level 1 22 19.8 7.2 Comparative Example 9 94.7 1.3 90.5 Level 1 20 19.6 7.2 Comparative Example 10 94.9 2.1 91.0 Level 2 15 18.8 7.3 Comparative Example 11 94.8 1.1 88.5 Level 1 18 19.0 7.2 Comparative Example 12 94.0 2.6 87.2 Level 2 20 19.8 7.1 Comparative Example 13 94.5 1.8 89.0 Level 1 23 19.5 7.2 The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A high-whiteness, yellowing-resistant rutile titanium dioxide, characterized in that, It includes a rutile titanium dioxide substrate, an inorganic composite coating layer covering the surface of the substrate, and an organic composite coating layer covering the outer surface of the inorganic composite coating layer; Based on 100 parts by weight of rutile titanium dioxide substrate, the inorganic composite coating layer comprises the following components in parts by weight: 2-6 parts of silicon compound coating component, 1-4 parts of zinc compound coating component, 3-8 parts of zirconium compound coating component, and 5-12 parts of aluminum compound coating component. The organic composite coating layer comprises the following components in parts by weight: 0.5-2 parts of silane coupling agent, 0.3-1.5 parts of polyether polyol, 0.2-1 parts of hindered amine light stabilizer, and 0.1-0.8 parts of pentaerythritol stearate.

2. The high whiteness and yellowing-resistant rutile titanium dioxide according to claim 1, characterized in that, The rutile titanium dioxide substrate is a primary rutile titanium dioxide product prepared by the sulfuric acid method or the chloride method, with a primary particle size of 0.2-0.35μm and a rutile crystal content of ≥98.5%.

3. The high whiteness and yellowing-resistant rutile titanium dioxide according to claim 1, characterized in that, The inorganic composite coating layers are, from the substrate outwards, a first inorganic coating layer, a second inorganic coating layer, and a third inorganic coating layer; The first inorganic coating layer is a composite dense layer of silicon compound and zinc compound, the second inorganic coating layer is a zirconium compound barrier layer, and the third inorganic coating layer is an aluminum compound buffer dispersion layer.

4. The high whiteness and yellowing-resistant rutile titanium dioxide according to claim 1, characterized in that, The silicon compound is at least one of sodium silicate, tetraethyl orthosilicate, and fumed silica. The zinc compound is at least one of zinc sulfate, zinc nitrate, and zinc oxide; The zirconium compound is at least one of zirconium oxychloride, zirconium sulfate, and zirconium nitrate; the aluminum compound is at least one of sodium aluminate, aluminum sulfate, and aluminum nitrate.

5. The high whiteness and yellowing-resistant rutile titanium dioxide according to claim 1, characterized in that, The silane coupling agent is at least one of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, and vinyltriethoxysilane. The polyether polyol is at least one of polypropylene glycol and polytetrahydrofuran ether glycol with a number average molecular weight of 2000-6000. The hindered amine light stabilizer is at least one of light stabilizer 944, light stabilizer 622, and light stabilizer 770.

6. The high whiteness and yellowing-resistant rutile titanium dioxide according to claim 1, characterized in that, The organic composite coating layer consists of a first organic coating layer and a second organic coating layer, arranged sequentially from the inorganic composite coating layer outwards. The first organic coating layer is an anchoring compatibility layer of silane coupling agent and polyether polyol, and the second organic coating layer is a functional lubricating layer of hindered amine light stabilizer and pentaerythritol stearate.

7. A method for preparing high-whiteness, yellowing-resistant rutile titanium dioxide as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Slurry preparation: Mix rutile titanium dioxide substrate with deionized water, add dispersant for high-speed dispersion, adjust the pH value of the slurry, and obtain a uniform titanium dioxide slurry. S2. Inorganic composite coating: The titanium dioxide slurry obtained in S1 is heated to a set temperature, and the first inorganic coating, the second inorganic coating, and the third inorganic coating are carried out in sequence. After each coating step is completed, constant temperature curing is performed to obtain inorganic coated titanium dioxide slurry. S3. Washing and drying: The inorganic coated titanium dioxide slurry obtained in S2 is washed and filtered by pressure. The filter cake is dried and pulverized to obtain inorganic coated titanium dioxide powder. S4. Organic composite coating: The inorganic coated titanium dioxide powder obtained in S3 is added to a high-speed mixer. After the temperature is increased by program, the first organic coating and the second organic coating are carried out in sequence. After each coating step is completed, constant temperature curing is carried out to obtain the organic coated powder. S5. Airflow milling: The organic-coated powder obtained in S4 is subjected to ultra-fine airflow milling to obtain the high-whiteness, yellowing-resistant rutile titanium dioxide.

8. The preparation method according to claim 7, characterized in that, In step S1, the solid content of the titanium dioxide slurry is 300-400 g / L, the dispersant is sodium hexametaphosphate, the amount added is 0.1-0.3% of the mass of the rutile titanium dioxide substrate, the high-speed dispersion time is 20-40 min, and the pH value of the slurry is adjusted to 9.0-10.0 using sodium hydroxide solution or sulfuric acid solution.

9. The preparation method according to claim 7, characterized in that, The specific operation of step S2 is as follows: S21. First inorganic coating: Heat the titanium dioxide slurry to 60-80℃, add a mixed aqueous solution of silicon compound and zinc compound at a uniform rate, and adjust the pH of the system to 8.0-9.5 with sulfuric acid solution. The feeding time is 60-120 min, and after the feeding is completed, it is kept at a constant temperature for 30-60 min. S22. Second inorganic coating: Add zirconium compound aqueous solution to the slurry after S21 curing at a uniform rate, while adjusting the pH of the system to 4.0-5.5 with sodium hydroxide solution. The feeding time is 40-90 min, and after the feeding is completed, the slurry is cured at a constant temperature for 20-40 min. S23. Third inorganic coating: Add an aqueous solution of aluminum compound to the slurry after S22 curing at a uniform rate, while adjusting the pH of the system to 6.5-7.5 with sulfuric acid solution or sodium hydroxide solution. The feeding time is 50-100 min, and after the feeding is completed, cure at a constant temperature for 40-80 min.

10. The preparation method according to claim 7, characterized in that, The specific operation of step S4 is as follows: S41. First organic coating: Add the inorganic coated titanium dioxide powder to a high-speed mixer, heat it to 80-100℃, add the preheated mixture of silane coupling agent and polyether polyol at a uniform speed, mix at high speed for 15-30 minutes to complete the first organic coating. S42. Second organic coating: Continue heating the system to 100-120℃, add the pre-molten hindered amine light stabilizer and pentaerythritol stearate mixture, mix at high speed for 20-40 min, and cure at constant temperature for 10-20 min to complete the second organic coating.