Preparation method of special titanium dioxide pigment for photovoltaic double-glass adhesive film

Abstract

A preparation method of a special titanium dioxide pigment for a photovoltaic double-glass adhesive film comprises the following steps: pulping a titanium dioxide primary product, adding a phosphate dispersant, curing, and grinding; the slurry is heated, and the whole coating process is carried out at the temperature. Adding a certain amount of phosphate solution and meta-aluminate solution in a parallel flow manner, controlling a certain pH value by using an acidic inorganic aluminum salt solution, and coating the surface of titanium dioxide with a first layer of aluminum phosphate film; adding a certain amount of water-soluble silicate and water-soluble magnesium salt, and controlling the pH value of the slurry by using an inorganic acid solution or an inorganic alkali solution to form a magnesium silicate film; filtering and washing with deionized water, drying, carrying out steam powder treatment, and adding a certain amount of vinyl trimethoxy silane in the steam powder treatment process; and recovering through a bag filter to obtain a final product. The titanium dioxide pigment prepared by the method is applied to a white adhesive film of a double-glass photovoltaic panel, has high light reflectivity and whiteness, and also has excellent light fastness and dispersion performance.

Description

Technical Field

[0001] This invention relates to a method for preparing a titanium dioxide pigment specifically for photovoltaic double-glass encapsulant films. Background Technology

[0002] With the continuous development of the photovoltaic industry, photovoltaic modules have been widely used in many fields such as building engineering. Double-glass photovoltaic panels are a common type of photovoltaic module, and with the increasing demands for their use, their performance is receiving more and more attention. Compared with single-glass photovoltaic panels, double-glass photovoltaic panels not only have higher weather resistance and corrosion resistance, but also have the advantages of higher power generation efficiency and longer service life. Their bifacial power generation design allows the photovoltaic panel to absorb sunlight from both the front and back sides, improving energy output. Depending on different ground environments, the power generation of double-glass photovoltaic panels can be increased by 10% to 30%. In addition, due to the excellent performance and low degradation rate of double-glass photovoltaic panels, their service life is also longer, generally reaching about 30 years. Therefore, double-glass photovoltaic panels are the development trend of the photovoltaic industry, accounting for more than 70% of the market.

[0003] Photovoltaic encapsulant film is mainly used in the encapsulation process of photovoltaic modules and is a key material for photovoltaic modules. The encapsulant film bonds photovoltaic cells to photovoltaic glass, protecting the cells and encapsulating them into photovoltaic modules that can output direct current. Titanium dioxide, due to its high refractive index, tinting strength, and hiding power, is the most widely used white pigment and is known as the "king of white pigments." Titanium dioxide is usually added to prepare white photovoltaic encapsulant film to improve light reflectivity and enhance the photoelectric conversion efficiency of the cells.

[0004] The requirements for the white encapsulant film used in single-glass and double-glass photovoltaic (PV) panels differ. White encapsulant films used in single-glass PV panels typically only require high whiteness, meaning high light refraction. However, white encapsulant films used in double-glass PV panels, in addition to high whiteness, also require excellent lightfastness. The titanium dioxide used in the white encapsulant film of single-glass PV panels often causes the film to turn bluish or blackish after exposure to light in double-glass PV panels. This difference is mainly due to the structural differences between single-glass and double-glass PV panels. The encapsulant film used in single-glass PV panels cannot completely isolate air, while the encapsulant film used in double-glass PV panels isolates air and creates an oxygen-deficient environment. When the white encapsulant film used in single-glass PV panels is exposed to sunlight or ultraviolet light, TiO2 undergoes a photochemical reaction, generating Ti... 3+ Unstable, it reacts with oxygen in the air to form Ti. 4+ The color of the adhesive film will not change. When the white adhesive film used in double-glass solar panels is exposed to sunlight or ultraviolet light, and TiO2 is in a closed, oxygen-deficient environment, Ti... 3+ (Gray) cannot be restored to Ti in time. 4+ As the exposure time to sunlight increases, Ti 3+As the buildup accumulates, the system's color becomes increasingly dull, and the corresponding encapsulant layer turns gray—this is the so-called aging process. The titanium dioxide used in single-glass encapsulants for photovoltaic double-glass films will turn gray and darken during application, which is a major challenge and pain point in applying titanium dioxide to photovoltaic double-glass encapsulants. Summary of the Invention

[0005] The main technical problem solved by this invention is to provide a method for preparing a titanium dioxide pigment for photovoltaic double-glass encapsulant film. The titanium dioxide pigment prepared by this method has high whiteness, high lightfastness, high reflectivity and excellent dispersibility in the white encapsulant film of double-glass photovoltaic panels.

[0006] The technical solution of this invention is: A method for preparing a titanium dioxide pigment specifically for photovoltaic double-glass encapsulant films includes the following steps: (1) Use rutile titanium dioxide primary product of chloride process, add deionized water to prepare titanium dioxide slurry, adjust the pH value of slurry to 8.5-10.0 with inorganic alkaline solution; add phosphate solution as dispersant, the amount of phosphate solution added is 0.1%-0.3% of the weight of P2O5 in phosphate to TiO2, and mature for 20-30 minutes; (2) Grind the matured titanium dioxide slurry and remove the grinding media from the water slurry; (3) Heat the ground slurry to 60℃~80℃ and maintain this temperature throughout the coating process; (4) Add phosphate solution within 1h to 2h, and add aluminate solution at the same time. The amount of phosphate solution added is 1.0% to 2.0% of the weight of P2O5 to TiO2, and the amount of aluminate solution added is 0.8% to 2.0% of the weight of Al2O3 to TiO2. Add acidic aluminum salt solution to control the pH value of the slurry at 7.0 to 9.0, and mature for 0.5h to 1h to form the first aluminum phosphate coating layer on the surface of titanium dioxide. (5) Add water-soluble silicate solution and water-soluble magnesium salt solution within 1h to 2h. The amount of water-soluble silicate solution added is 1.0% to 3.0% based on the weight of SiO2 in water-soluble silicate and 0.5% to 1.5% based on the weight of MgO in water-soluble magnesium salt. At the same time, use inorganic acid or inorganic alkaline solution to control the pH value of the slurry to 8.0 to 11.0 and mature for 1h to 2h. (6) Wash with deionized water at 50℃~80℃ until the conductivity of the filter cake is greater than 8000Ω·cm, then dry and steam powder treatment. During the steam powder treatment, add 0.2%~1.0% of vinyltrimethoxysilane by weight of TiO2. Collect through bag filter and package to obtain photovoltaic double glass special titanium dioxide.

[0007] Further, the phosphate mentioned in steps (1) and (4) is at least one of sodium hexametaphosphate, sodium pyrophosphate, sodium tripolyphosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, or phosphoric acid; wherein the solution concentration of the phosphate is 100 g / L to 200 g / L, calculated as P2O5.

[0008] Further, in step (4), the aluminate solution is at least one of sodium aluminate solution and potassium aluminate solution, and the concentration of the aluminate solution is 100g / L to 200g / L based on Al2O3 in the aluminate.

[0009] Further, the acidic aluminum salt solution in step (4) is at least one of aluminum sulfate solution and aluminum chloride solution, and the concentration of the acidic aluminum salt solution is 50 g / L to 100 g / L based on Al2O3 in the acidic aluminum salt.

[0010] Further, in step (5), the water-soluble silicate is selected from at least one of sodium silicate and potassium silicate, and the concentration of the water-soluble silicate solution is 150 g / L to 250 g / L based on SiO2; the water-soluble magnesium salt is at least one of magnesium chloride and magnesium sulfate, and the concentration of the water-soluble magnesium salt solution is 50 g / L to 150 g / L based on MgO. Furthermore, the mass ratio of SiO2 in water-soluble silicates to MgO in water-soluble magnesium salts is 2:1.

[0011] Further, in steps (1) and (5), the inorganic alkaline solution is at least one of sodium hydroxide solution and potassium hydroxide solution, and the mass concentration of the inorganic alkaline solution is 20% to 40%. In step (5), the inorganic acid is at least one of hydrochloric acid, sulfuric acid, and nitric acid.

[0012] Furthermore, after the titanium dioxide slurry is ground, the mass content of titanium dioxide slurry with D50 ≤ 500nm and D99 > 800nm ​​is ≤ 1.0%.

[0013] Furthermore, the concentration of the titanium dioxide slurry is 500 g / L to 800 g / L.

[0014] Compared with the prior art, the beneficial effects of the present invention are: This invention uses rutile titanium dioxide oxide precursor produced by the chloride process as the raw material for preparing the target product. The particles have a high proportion of near-spherical shapes and a good particle size distribution, which can effectively improve the whiteness, hiding power and weather resistance of the final product, thereby improving the photoelectric conversion efficiency of the solar cell.

[0015] The product prepared by this invention adopts a three-layer coating combination, wherein: The first layer uses a hydrated aluminum phosphate coating, which not only effectively blocks the photochemical spots of the product but also ensures that the film product has excellent lightfastness. The principle is as follows: when a dense layer of phosphorus compound (aluminum phosphate) is coated on the surface of titanium dioxide, the prepared white film is exposed to sunlight or ultraviolet light, and the TiO2 in the film generates Ti... 3+ In an oxygen-deficient environment, Ti 3+ They seized the PO 4+ The oxygen in the oxygen reduces aluminum phosphate to aluminum phosphite. Since aluminum phosphite is white or transparent, it has little effect on the whiteness of TiO2. However, when a large amount of PO3 is produced... 3- At that time, PO3 3- It can also combine with OH• produced by the photochemical reaction of TiO2 to form PO4. 3- This prevents chemically active OH• from flowing into the organic matrix surrounding TiO2, thus avoiding oxidative degradation of the organic matrix and extending the product's lifespan. The second layer uses hydrated magnesium silicate coating. The successful introduction of hydrated magnesium silicate coating layer as the second main film layer can not only solve the thixotropy of the final product and ensure the feasibility of the production process, but also, most importantly, the prepared product has high whiteness, which can improve the light reflection of the film product and improve the photoelectric conversion efficiency of the battery cell. The third layer uses organosilicon. A certain amount of vinyltrimethoxysilane is added during the powder coating process to coat the surface of titanium dioxide with a third organosilicon film. This film not only ensures that the final product is hydrophobic, but also effectively improves the compatibility and dispersibility of titanium dioxide in the photovoltaic film, ensuring that the film product reflects light further, thereby improving the photoelectric conversion efficiency of the solar cell.

[0016] The titanium dioxide pigment prepared by this invention has high whiteness, high lightfastness, high reflectivity and excellent dispersibility, making it most suitable for use in double-glass photovoltaic films. Detailed Implementation

[0017] The present invention will be further described below with reference to specific embodiments. However, the application scope of the present invention is not limited to the embodiments. Various substitutions and modifications made without departing from the technical concept of the present invention should be within the scope of the present invention.

[0018] Example 1 1.1 Weigh 400g of rutile titanium dioxide raw powder prepared by the chlorination method, add deionized water to prepare a slurry with a concentration of 500g / L. The pH value of the slurry is measured by pH meter throughout the coating process. The pH of the slurry is adjusted to 8.5 with 20% sodium hydroxide solution. Sodium tripolyphosphate solution is added. The concentration of sodium tripolyphosphate solution is 100g / L based on P2O5. The amount of sodium tripolyphosphate solution added is 0.1% based on the weight of P2O5 in sodium tripolyphosphate and TiO2. Let it mature for 20min. 1.2 The matured titanium dioxide slurry was ground, and the mass content of the slurry with D50 at 380 nm and D99 exceeding 800 nm was 0.8%, and the grinding media was removed from the water slurry. 1.3 Heat the slurry after sand milling to 60°C and maintain this temperature throughout the coating process; 1.4 Add sodium tripolyphosphate solution with a weight of 1.0% P2O5 based on TiO2 and a sodium tripolyphosphate concentration of 100 g / L based on P2O5 within 1 hour. Simultaneously add sodium aluminate solution with a weight of 0.8% Al2O3 based on TiO2 and a sodium aluminate concentration of 100 g / L based on Al2O3. Add aluminum sulfate solution to control the pH value at 7.0 and the aluminum sulfate concentration of 50 g / L based on Al2O3. Let it mature for 0.5 hours to form the first aluminum phosphate coating layer on the surface of titanium dioxide. 1.5 Add water-soluble sodium silicate solution and water-soluble magnesium sulfate solution within 1 hour. The amount added is 1.0% of the weight of SiO2 as TiO2, the concentration of water-soluble sodium silicate solution is 150 g / L based on SiO2, the amount added of water-soluble magnesium sulfate solution is 0.5% of the weight of MgO as TiO2, and the concentration of water-soluble magnesium sulfate solution is 50 g / L based on MgO. At the same time, adjust the pH value of the slurry to 8.0 with a 20% (w / w) sodium hydroxide solution and mature for 1 hour. 1.6 The above slurry is washed with deionized water at 60°C until the filter cake conductivity is 12000Ω·cm, then dried and treated with steam powder. During the steam powder treatment, 0.2% vinyltrimethoxysilane (based on the weight of vinyltrimethoxysilane as a percentage of TiO2) is added. The mixture is collected through a bag filter and packaged to obtain a special titanium dioxide pigment for photovoltaic double glass film.

[0019] Example 2 1.1 Weigh 400g of rutile titanium dioxide raw powder prepared by the chlorination method, add deionized water to prepare a slurry with a concentration of 800g / L. The pH value of the slurry is measured by pH meter throughout the coating process. The pH of the slurry is adjusted to 10.0 with 40% potassium hydroxide solution. Sodium pyrophosphate solution is added. The concentration of sodium pyrophosphate solution is 200g / L based on P2O5. The amount of sodium pyrophosphate solution added is 0.3% based on the weight of P2O5 in sodium pyrophosphate and TiO2. Let it mature for 30min. 1.2 The above-mentioned matured titanium dioxide slurry is ground, and the mass content of the slurry with D50 at 450nm and D99 exceeding 800nm ​​is 0.95%, and the grinding media is removed from the water slurry. 1.3 Heat the slurry after sand milling to 80°C and maintain this temperature throughout the coating process; 1.4 Within 2 hours, add a sodium pyrophosphate solution with a P2O5 content of 2.0% by weight of TiO2 and a sodium pyrophosphate solution concentration of 200 g / L based on P2O5. Simultaneously, add a potassium aluminate solution with an Al2O3 content of 2.0% by weight of TiO2 and a potassium aluminate solution concentration of 200 g / L based on Al2O3. Add an aluminum chloride solution to control the pH value at 9.0 and an aluminum chloride solution concentration of 100 g / L based on Al2O3. Allow to mature for 1.0 hour to form a first aluminum phosphate coating layer on the surface of titanium dioxide. 1.5 Add water-soluble potassium silicate solution and water-soluble magnesium chloride solution within 2 hours. The amount added is 3.0% of the weight of SiO2 as TiO2, the concentration of water-soluble potassium silicate solution is 250 g / L based on SiO2, the amount added of water-soluble magnesium chloride solution is 1.5% of the weight of MgO as TiO2, and the concentration of water-soluble magnesium chloride solution is 150 g / L based on MgO. At the same time, adjust the pH value of the slurry to 11.0 with a 40% potassium hydroxide solution and let it mature for 2 hours. 1.6 The above slurry is washed with deionized water at 80°C until the filter cake conductivity is 85000Ω·cm, then dried and treated with steam powder. During the steam powder treatment, 1.0% vinyltrimethoxysilane (based on the weight of vinyltrimethoxysilane as a percentage of TiO2) is added. The mixture is collected through a bag filter and packaged to obtain a special titanium dioxide pigment for photovoltaic double-glass film.

[0020] Example 3 1.1 Weigh 400g of rutile titanium dioxide raw powder prepared by the chlorination method, add deionized water to prepare a slurry with a concentration of 600g / L. The pH value of the slurry was measured with a pH meter throughout the coating process. The pH of the slurry was adjusted to 9.0 with a 30% sodium hydroxide solution. Sodium hexametaphosphate solution was added. The concentration of sodium hexametaphosphate solution was 150g / L based on P2O5. The amount of sodium hexametaphosphate solution added was 0.2% based on the weight of P2O5 in sodium hexametaphosphate and TiO2. The mixture was allowed to mature for 25min. 1.2 The above-mentioned matured titanium dioxide slurry is ground, and the mass content of the slurry with D50 at 400 nm and D99 exceeding 800 nm is 0.9%, and the grinding media is removed from the water slurry. 1.3 Heat the slurry after sand milling to 70°C and maintain this temperature throughout the coating process; 1.4 Within 1.5 hours, add a sodium hexametaphosphate solution with a P2O5 content of 1.5% of TiO2 by weight, and the sodium hexametaphosphate solution concentration is 150 g / L based on P2O5. Simultaneously, add a sodium aluminate solution with an Al2O3 content of 1.5% of TiO2 by weight, and the sodium aluminate solution concentration is 200 g / L based on Al2O3. Add an aluminum sulfate solution to control the pH value at 8.5, and the aluminum sulfate solution concentration is 100 g / L based on Al2O3. After aging for 1.0 hour, an aluminum phosphate first coating layer is formed on the surface of titanium dioxide. 1.5 Add water-soluble sodium silicate solution and water-soluble magnesium sulfate solution within 2 hours. The amount added is 2.0% of the weight of SiO2 as TiO2, the concentration of water-soluble sodium silicate solution is 200 g / L based on SiO2, the amount added of water-soluble magnesium sulfate solution is 1.0% of the weight of MgO as TiO2, and the concentration of water-soluble magnesium sulfate solution is 100 g / L based on MgO. At the same time, adjust the pH value of the slurry to 9.5 with a 30% sodium hydroxide solution and let it mature for 1.5 hours. 1.6 The above slurry is washed with deionized water at 70°C until the filter cake conductivity is 10000Ω·cm, then dried and treated with steam powder. During the steam powder treatment, 0.5% vinyltrimethoxysilane (based on the weight of vinyltrimethoxysilane as a percentage of TiO2) is added. The mixture is collected through a bag filter and packaged to obtain a special titanium dioxide pigment for photovoltaic double-glass film.

[0021] Comparative Example 1 Similar to Example 3, except for step 1.4 in Example 3: Within 1.5 hours, add a sodium hexametaphosphate solution with a P2O5 content of 1.5% of TiO2 by weight, the concentration of which is 150 g / L (based on P2O5); simultaneously add a sodium aluminate solution with an Al2O3 content of 1.5% of TiO2 by weight, the concentration of which is 200 g / L (based on Al2O3); add an aluminum sulfate solution to control the pH at 8.5, the concentration of which is 100 g / L (based on Al2O3); and allow to mature for 1.0 hour to form a first aluminum phosphate coating layer on the titanium dioxide surface; the steps are as follows: 1.1 Weigh 400g of rutile titanium dioxide raw powder prepared by the chlorination method, add deionized water to prepare a slurry with a concentration of 600g / L. The pH value of the slurry was measured with a pH meter throughout the coating process. The pH of the slurry was adjusted to 9.0 with a 30% sodium hydroxide solution. Sodium hexametaphosphate solution was added. The concentration of sodium hexametaphosphate solution was 150g / L based on P2O5. The amount of sodium hexametaphosphate solution added was 0.2% based on the weight of P2O5 in sodium hexametaphosphate and TiO2. The mixture was allowed to mature for 25min. 1.2 The above-mentioned matured titanium dioxide slurry is ground, and the mass content of the slurry with D50 at 400 nm and D99 exceeding 800 nm is 0.9%, and the grinding media is removed from the water slurry. 1.3 Heat the slurry after sand milling to 70°C and maintain this temperature throughout the coating process; 1.4 Add water-soluble sodium silicate solution and water-soluble magnesium sulfate solution within 2 hours. The amount added is 2.0% of the weight of SiO2 as TiO2, the concentration of water-soluble sodium silicate solution is 200 g / L based on SiO2, the amount added of water-soluble magnesium sulfate solution is 1.0% of the weight of MgO as TiO2, and the concentration of water-soluble magnesium sulfate solution is 100 g / L based on MgO. At the same time, adjust the pH of the slurry to 9.5 with a 30% sodium hydroxide solution and let it mature for 1.5 hours. 1.5 The above slurry is washed with deionized water at 70°C until the filter cake conductivity is 10000Ω·cm, then dried and treated with steam powder. During the steam powder treatment, 0.5% vinyltrimethoxysilane (based on the weight of vinyltrimethoxysilane as a percentage of TiO2) is added. The mixture is collected through a bag filter and packaged to obtain titanium dioxide pigment.

[0022] Comparative Example 2 Only step 1.5 in Example 3 is omitted: Water-soluble sodium silicate solution and water-soluble magnesium sulfate solution are added within 2 hours. The amount added is 2.0% of the weight of SiO2 in TiO2, the concentration of the water-soluble sodium silicate solution is 200 g / L (based on SiO2), the amount added of the water-soluble magnesium sulfate solution is 1.0% of the weight of MgO in TiO2, and the concentration of the water-soluble magnesium sulfate solution is 100 g / L (based on MgO). Simultaneously, the pH of the slurry is adjusted to 9.5 with a 30% sodium hydroxide solution, and the slurry is matured for 1.5 hours. The steps are as follows: 1.1 Weigh 400g of rutile titanium dioxide raw powder prepared by the chlorination method, add deionized water to prepare a slurry with a concentration of 600g / L. The pH value of the slurry was measured with a pH meter throughout the coating process. The pH of the slurry was adjusted to 9.0 with a 30% sodium hydroxide solution. Sodium hexametaphosphate solution was added. The concentration of sodium hexametaphosphate solution was 150g / L based on P2O5. The amount of sodium hexametaphosphate solution added was 0.2% based on the weight of P2O5 in sodium hexametaphosphate and TiO2. The mixture was allowed to mature for 25min. 1.2 The above-mentioned matured titanium dioxide slurry is ground, and the mass content of the slurry with D50 at 400 nm and D99 exceeding 800 nm is 0.9%, and the grinding media is removed from the water slurry. 1.3 Heat the slurry after sand milling to 70°C and maintain this temperature throughout the coating process; 1.4 Within 1.5 hours, add a sodium hexametaphosphate solution with a P2O5 content of 1.5% of TiO2 by weight, and the sodium hexametaphosphate solution concentration is 150 g / L based on P2O5. Simultaneously, add a sodium aluminate solution with an Al2O3 content of 1.5% of TiO2 by weight, and the sodium aluminate solution concentration is 200 g / L based on Al2O3. Add an aluminum sulfate solution to control the pH value at 8.5, and the aluminum sulfate solution concentration is 100 g / L based on Al2O3. After aging for 1.0 hour, an aluminum phosphate first coating layer is formed on the surface of titanium dioxide. 1.5 The above slurry is washed with deionized water at 70°C until the filter cake conductivity is 10000Ω·cm, then dried and treated with steam powder. During the steam powder treatment, 0.5% vinyltrimethoxysilane (based on the weight of vinyltrimethoxysilane as a percentage of TiO2) is added. The mixture is collected through a bag filter and packaged to obtain titanium dioxide pigment.

[0023] Comparative Example 3 1.1 Weigh 400g of rutile titanium dioxide raw powder prepared by the chlorination method, add deionized water to prepare a slurry with a concentration of 600g / L. The pH value of the slurry was measured with a pH meter throughout the coating process. The pH of the slurry was adjusted to 9.0 with a 30% sodium hydroxide solution. Sodium hexametaphosphate solution was added. The concentration of sodium hexametaphosphate solution was 150g / L based on P2O5. The amount of sodium hexametaphosphate solution added was 0.2% based on the weight of P2O5 in sodium hexametaphosphate and TiO2. The mixture was allowed to mature for 25min. 1.2 The above-mentioned matured titanium dioxide slurry is ground, and the mass content of the slurry with D50 at 400 nm and D99 exceeding 800 nm is 0.9%, and the grinding media is removed from the water slurry. 1.3 Heat the slurry after sand milling to 70°C and maintain this temperature throughout the coating process; 1.4 Within 1.5 hours, add a sodium hexametaphosphate solution with a P2O5 content of 1.5% of TiO2 by weight, and the sodium hexametaphosphate solution concentration is 150 g / L based on P2O5. Simultaneously, add a sodium aluminate solution with an Al2O3 content of 1.5% of TiO2 by weight, and the sodium aluminate solution concentration is 200 g / L based on Al2O3. Add an aluminum sulfate solution to control the pH value at 8.5, and the aluminum sulfate solution concentration is 100 g / L based on Al2O3. After aging for 1.0 hour, an aluminum phosphate first coating layer is formed on the surface of titanium dioxide. 1.5 Add water-soluble sodium silicate solution and water-soluble magnesium sulfate solution within 2 hours. The amount added is 2.0% of the weight of SiO2 as TiO2, the concentration of water-soluble sodium silicate solution is 200 g / L based on SiO2, the amount added of water-soluble magnesium sulfate solution is 1.0% of the weight of MgO as TiO2, and the concentration of water-soluble magnesium sulfate solution is 100 g / L based on MgO. At the same time, adjust the pH value of the slurry to 9.5 with a 30% sodium hydroxide solution and let it mature for 1.5 hours. 1.6 The above slurry is washed with deionized water at 70°C until the conductivity of the filter cake is 10000Ω·cm, then dried and treated with steam powder. After being collected through a bag filter and packaged, titanium dioxide pigment is obtained.

[0024] Comparative Example 4 1.1 Weigh 400g of rutile titanium dioxide raw powder prepared by the sulfuric acid method, add deionized water to prepare a slurry with a concentration of 600g / L. The pH value of the slurry was measured with a pH meter throughout the coating process. The pH of the slurry was adjusted to 10.0 with a 30% sodium hydroxide solution. Sodium hexametaphosphate solution was added. The concentration of sodium hexametaphosphate solution was 150g / L based on P2O5. The amount of sodium hexametaphosphate solution added was 0.2% based on the weight of P2O5 in sodium hexametaphosphate and TiO2. The mixture was allowed to mature for 25min. 1.2 The above-mentioned matured titanium dioxide slurry is ground, and the mass content of the slurry with D50 at 400 nm and D99 exceeding 800 nm is 0.9%, and the grinding media is removed from the water slurry. 1.3 Heat the slurry after sand milling to 70°C and maintain this temperature throughout the coating process; 1.4 Within 1.5 hours, add a sodium hexametaphosphate solution with a P2O5 content of 1.5% of TiO2 by weight, and the sodium hexametaphosphate solution concentration is 150 g / L based on P2O5. Simultaneously, add a sodium aluminate solution with an Al2O3 content of 1.5% of TiO2 by weight, and the sodium aluminate solution concentration is 200 g / L based on Al2O3. Add an aluminum sulfate solution to control the pH value at 8.5, and the aluminum sulfate solution concentration is 100 g / L based on Al2O3. After aging for 1.0 hour, an aluminum phosphate first coating layer is formed on the surface of titanium dioxide. 1.5 Add water-soluble sodium silicate solution and water-soluble magnesium sulfate solution within 2 hours. The amount added is 2.0% of the weight of SiO2 as TiO2, the concentration of water-soluble sodium silicate solution is 200 g / L based on SiO2, the amount added of water-soluble magnesium sulfate solution is 1.0% of the weight of MgO as TiO2, and the concentration of water-soluble magnesium sulfate solution is 100 g / L based on MgO. At the same time, adjust the pH value of the slurry to 9.5 with a 30% sodium hydroxide solution and let it mature for 1.5 hours. 1.6 The above slurry is washed with deionized water at 70°C until the filter cake conductivity is 10000Ω·cm, then dried and treated with steam powder. During the steam powder treatment, 0.5% vinyltrimethoxysilane (based on the weight of vinyltrimethoxysilane as a percentage of TiO2) is added. The mixture is collected through a bag filter and packaged to obtain titanium dioxide pigment.

[0025] The test results of the titanium dioxide pigments prepared in Examples 1-3 and Comparative Examples 1-4 are shown in Table 1. Lab was determined according to GB / T 5211.20-1999; the dispersibility was determined by the pressure filtration value (PF value) method according to EN13900-5:2005; the lightfastness test method was as follows: a certain amount of fiber was added to water and placed in a descaling apparatus to ensure that the pulp moisture content was 90%wt. Titanium dioxide, fiber and various reagents were mixed and pulped to make decorative base paper. The weight and ash content of the paper were measured; melamine impregnation and pressing were carried out, and the pressing plates were placed in a UV aging chamber for light stability testing. The Lab before and after exposure was tested, and the color difference (∆E) of the paper pressing plates was calculated.

[0026] Table 1 shows the relevant and application indicators of the products in the examples. The comparison of Examples 1-3 in the table above shows that the relevant indicators of the three samples, such as brightness, hue, dispersibility, and lightfastness, are quite similar. Generally, brightness (L*) is related to whiteness; the higher the L*, the higher the whiteness. The higher the hue (b*), the yellower the hue, and the lower the whiteness of the product. Dispersibility directly affects the processing performance of titanium dioxide and the whiteness and hiding power of the white film; the lower the dispersibility value, the better the processing performance, and the better the whiteness and hiding power of the white film product. Lightfastness is the most important for double-glazed white films; the quality of lightfastness directly affects the reflectivity and service life of the white film product. The lower the lightfastness (∆E) value, the better the lightfastness.

[0027] The comparison results between Comparative Example 1 and Example 3 show that the lightfastness of the product deteriorates significantly after the first layer of aluminum phosphate film is removed, indicating that the innermost layer of aluminum phosphate film is crucial for improving the lightfastness of the product.

[0028] The comparison results between Comparative Example 2 and Example 3 show that the L* of the product decreased after the second layer of magnesium silicate film was removed, indicating that the magnesium silicate film has a certain effect on improving the L* of the product. In addition, it also improves the lightfastness of the product.

[0029] The comparison results between Comparative Example 3 and Example 3 show that the product's dispersibility is significantly worse when the third silicone coating layer is removed, which has a great impact on the production and preparation of white film products. If the titanium dioxide product cannot be evenly dispersed in the white film, it will also have an adverse effect on the reflectivity and hiding power of the film product.

[0030] The comparison results between Comparative Example 4 and Example 3 show that the product L* prepared using the sulfuric acid process as the base material is significantly lower than that prepared using the chloride process as the base material, and the product b* prepared is also significantly higher than that of Example 3. This indicates that the product prepared using the sulfuric acid process as the base material has a significantly yellowish hue, which also affects the light reflection of the white film.

[0031] Therefore, it can be seen that the titanium dioxide pigment produced according to the specific preparation method of the present invention has the characteristics of high light resistance, high whiteness and excellent dispersibility in photovoltaic double glass white film, and is the best choice of titanium dioxide pigment required in this field.

Claims

1. A method for preparing a titanium dioxide pigment specifically for photovoltaic double-glass encapsulant films, characterized in that: Includes the following steps: (1) Use rutile titanium dioxide primary product of chloride process, add deionized water to prepare titanium dioxide slurry, adjust the pH value of slurry to 8.5-10.0 with inorganic alkaline solution; add phosphate solution as dispersant, the amount of phosphate solution added is 0.1%-0.3% of the weight of P2O5 in phosphate to TiO2, and mature for 20-30 minutes; (2) Grind the matured titanium dioxide slurry and remove the grinding media from the water slurry; (3) Heat the ground slurry to 60℃~80℃ and maintain this temperature throughout the coating process; (4) Add phosphate solution within 1h to 2h, and add aluminate solution at the same time. The amount of phosphate solution added is 1.0% to 2.0% of the weight of P2O5 to TiO2, and the amount of aluminate solution added is 0.8% to 2.0% of the weight of Al2O3 to TiO2. Add acidic aluminum salt solution to control the pH value of the slurry at 7.0 to 9.0, and mature for 0.5h to 1h to form the first aluminum phosphate coating layer on the surface of titanium dioxide. (5) Add water-soluble silicate solution and water-soluble magnesium salt solution within 1h to 2h. The amount of water-soluble silicate solution added is 1.0% to 3.0% based on the weight of SiO2 in water-soluble silicate and 0.5% to 1.5% based on the weight of MgO in water-soluble magnesium salt. At the same time, use inorganic acid or inorganic alkaline solution to control the pH value of the slurry to 8.0 to 11.0 and mature for 1h to 2h. (6) Wash with deionized water at 50℃~80℃ until the conductivity of the filter cake is greater than 8000Ω·cm, then dry and steam powder treatment. During the steam powder treatment, add 0.2%~1.0% of vinyltrimethoxysilane by weight of TiO2. Collect through bag filter and package to obtain photovoltaic double glass special titanium dioxide.

2. The preparation method of the photovoltaic double-glass encapsulant film-specific titanium dioxide pigment according to claim 1, characterized in that: The phosphates mentioned in steps (1) and (4) are at least one of sodium hexametaphosphate, sodium pyrophosphate, sodium tripolyphosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, or phosphoric acid; wherein the concentration of the phosphate solution, calculated as P2O5, is 100 g / L to 200 g / L.

3. The preparation method of the special titanium dioxide pigment for photovoltaic double-glass encapsulant film according to claim 1, characterized in that: In step (4), the aluminate solution is at least one of sodium aluminate solution and potassium aluminate solution, and the concentration of the aluminate solution is 100g / L to 200g / L based on Al2O3 in the aluminate.

4. The method for preparing the special titanium dioxide pigment for photovoltaic double-glass encapsulant film according to claim 1, characterized in that: The acidic aluminum salt solution in step (4) is at least one of aluminum sulfate solution and aluminum chloride solution, and the concentration of the acidic aluminum salt solution is 50 g / L to 100 g / L based on Al2O3 in the acidic aluminum salt.

5. The preparation method of the photovoltaic double-glass encapsulant film-specific titanium dioxide pigment according to claim 1, characterized in that: In step (5), the water-soluble silicate is selected from at least one of sodium silicate and potassium silicate, and the concentration of the water-soluble silicate solution is 150 g / L to 250 g / L based on SiO2; the water-soluble magnesium salt is at least one of magnesium chloride and magnesium sulfate, and the concentration of the water-soluble magnesium salt solution is 50 g / L to 150 g / L based on MgO.

6. The method for preparing the special titanium dioxide pigment for photovoltaic double-glass encapsulant film according to claim 1, characterized in that: The mass ratio of SiO2 in water-soluble silicates to MgO in water-soluble magnesium salts is 2:

1.

7. The method for preparing the special titanium dioxide pigment for photovoltaic double-glass encapsulant film according to claim 1, characterized in that: In steps (1) and (5), the inorganic alkaline solution is at least one of sodium hydroxide solution and potassium hydroxide solution, and the mass concentration of the inorganic alkaline solution is 20% to 40%. In step (5), the inorganic acid is at least one of hydrochloric acid, sulfuric acid, and nitric acid.

8. The method for preparing the special titanium dioxide pigment for photovoltaic double-glass encapsulant film according to claim 1, characterized in that: After grinding, the mass content of titanium dioxide slurry with D50 ≤ 500nm and D99 > 800nm ​​is ≤ 1.0%.

9. The method for preparing the special titanium dioxide pigment for photovoltaic double-glass encapsulant film according to claim 1, characterized in that: The concentration of the titanium dioxide slurry is 500 g / L to 800 g / L.

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