Preparation method and application of phosphorus-aluminum coating agent

Abstract

The application discloses a preparation method and application of a phosphorus-aluminum coating agent, and belongs to the technical field of titanium dioxide preparation. The existing sodium metaaluminate prepared by using aluminum hydroxide and sodium hydroxide is used as a coating agent. However, in order to adjust pH in the coating process, the use of sulfuric acid to neutralize sodium hydroxide causes the problems of cost increase and salt discharge increase. The aluminum hydroxide is reacted with phosphoric acid to generate a soluble salt, which is used for surface treatment of titanium dioxide. The purpose is that the aluminum hydroxide is reacted with the phosphoric acid to form the soluble aluminum phosphate salt, which is used as a coating agent for surface treatment of the titanium dioxide, so that the problem of cost increase caused by the use of sulfuric acid to neutralize sodium hydroxide in order to adjust pH in the coating process is avoided.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of titanium dioxide preparation, and particularly relates to a preparation method and application of a phosphorus-aluminum coating agent. BACKGROUND

[0002] The surface properties of titanium dioxide are closely related to the production method, surface coating process and coating effect, which further affect the dispersion, gloss, weather resistance and oil absorption of the titanium dioxide in the application system. At present, the surface treatment methods of titanium dioxide can be divided into two categories: inorganic surface treatment and organic surface treatment. Inorganic surface treatment generally coats one or more layers of inorganic hydrated oxide film on the surface of titanium dioxide particles through precipitation and adsorption. Through inorganic surface coating, the crystal lattice defects of titanium dioxide can be blocked, thereby improving the weather resistance of titanium dioxide particles. Most of the existing decorative laminated paper uses LR-952 titanium dioxide, which is coated with phosphoric acid and sodium metaaluminate to improve the light resistance of the product in the decorative laminated paper. Since the product has been put on the market, the light resistance in the laminated paper has been widely recognized by customers. At present, sodium metaaluminate is generally prepared by the reaction of aluminum hydroxide and sodium hydroxide. In order to avoid decomposition, the content of sodium hydroxide in sodium metaaluminate is excessive, and dilute sulfuric acid needs to be used for further neutralization. After neutralization, sodium sulfate solution is generated, which is discharged to the sewage station through three washings, thereby greatly increasing the cost of the entire neutralization reaction. SUMMARY

[0003] In view of the problems in the prior art, the application provides a preparation method and application of a phosphorus-aluminum coating agent. Aluminum hydroxide is an amphoteric compound which can react with acid to generate a soluble salt. Aluminum hydroxide reacts with phosphoric acid to form aluminum phosphate, a soluble salt, which is used as a coating agent for the surface treatment of titanium dioxide. The problems of using sodium metaaluminate prepared from aluminum hydroxide and sodium hydroxide as a coating agent, but increasing the cost due to the use of sulfuric acid to neutralize sodium hydroxide in order to adjust the pH during the coating process, are avoided.

[0004] The technical scheme adopted by the application is as follows:

[0005] A preparation method of a phosphorus-aluminum coating agent, characterized in that the method comprises the following steps:

[0006] Step 1: mixing phosphoric acid and aluminum hydroxide to obtain a mixture A;

[0007] Step 2: aging the mixture A for a certain time to obtain a mixture B;

[0008] Step 3: adding dilute water to the mixture B to obtain the phosphorus-aluminum coating agent.

[0009] Preferably, in step 1, the addition amount of phosphoric acid is 6.2 m 3 , and the addition amount of aluminum hydroxide is 2 t.

[0010] Preferably, the phosphoric acid is added in a ratio of 3:1 to aluminum hydroxide.

[0011] Preferably, the mixture A in step 2 is aged for 55-65 minutes.

[0012] Preferably, in step 3, dilute water is added until the concentration is 100-120 g / L as P2O5.

[0013] Preferably, a method for coating titanium dioxide with a phosphorus-aluminum coating agent comprises the phosphorus-aluminum coating agent of claims 1-4, and comprises the following steps:

[0014] Step A: A predetermined amount of titanium dioxide slurry is poured into a coating device, and after stirring, the concentration is measured and adjusted to within the acceptable range to obtain slurry A;

[0015] Step B: The phosphorus-aluminum coating agent is added to the slurry A, and the pH is adjusted, and after aging, slurry B is obtained;

[0016] Step C: The phosphorus-aluminum coating agent and sodium metaaluminate solution are added to the slurry B in parallel flow, and after aging, slurry C is obtained;

[0017] Step D: The sodium metaaluminate solution is added to the slurry C, and after aging, slurry D is obtained;

[0018] Step E: The aluminum sulfate solution and sodium metaaluminate solution are added to the slurry D in parallel flow, and after aging, slurry E is obtained;

[0019] Step F: The pH of the slurry E is adjusted to obtain the coated titanium dioxide slurry.

[0020] Preferably, the pH of the slurry B obtained after aging is 6.0-6.5.

[0021] Preferably, the total mass of the phosphorus-aluminum coating agent added in steps B and C is 2.2-3:1 to the titanium dioxide as P2O5, and the pH of the slurry C obtained after aging is controlled to be 6.0-7.5.

[0022] Preferably, the pH of the slurry D obtained after aging is 8.0-8.5.

[0023] Preferably, the total mass of the sodium metaaluminate and aluminum sulfate added in steps C, D, and E is 5.0-6.0:1 to the titanium dioxide as Al2O3, and the pH of the slurry E obtained after aging is 8.0-8.5.

[0024] Preferably, the pH of the coated titanium dioxide slurry obtained in step F is 5.5-6.0.

[0025] In summary, due to the use of the above technical solutions, the present application has the following advantages:

[0026] 1. The aluminum hydroxide is an amphoteric compound, which can react with acid to generate soluble salt, the aluminum hydroxide reacts with phosphoric acid to form aluminum phosphate, which is a soluble salt, and is used as a coating agent for the surface treatment of titanium dioxide, which avoids the problem of using sodium metaaluminate prepared by using aluminum hydroxide and sodium hydroxide as a coating agent, but in the coating process, in order to adjust the pH, the use of sulfuric acid to neutralize sodium hydroxide causes the problem of cost increase;

[0027] 2. The application reduces the problem of neutralizing sodium hydroxide by sulfuric acid, and reduces the emission of salt content;

[0028] 3. The aluminum phosphate film layer is relatively dense, which can improve the hydrophilic property of the pigment, improve the retention rate in the paper system, and enhance the light resistance of the laminated paper, when aluminum or aluminum compound reacts with phosphoric acid, short chains between oxygen, phosphorus and aluminum atoms can be formed, by increasing the pH value of the reaction system, the short chains can be quickly condensed into long chains to form a network body, which has high surface affinity and can cover other pigments, thereby improving the lightness of titanium dioxide, and the improvement of lightness can improve the light resistance, weather resistance and hiding power of titanium dioxide, and improve the whiteness and gloss of the product, and it is not easy to discolor or decompose under ultraviolet light;

[0029] 4. In the traditional treatment process, due to the excessive sodium hydroxide in sodium metaaluminate, dilute sulfuric acid is needed for further neutralization, which may cause the rebound of pH value, that is, the pH value is unstable after treatment, and after using the phosphorus aluminum coating agent, since it directly reacts with aluminum hydroxide to form aluminum phosphate, this direct reaction avoids the additional neutralization step, thereby eliminating the rebound of pH value;

[0030] 5. The application accurately controls the addition amount of phosphorus aluminum coating agent, aluminum sulfate solution and sodium metaaluminate solution in each step in the coating process, which saves the cost and maximizes the light resistance of the laminated paper after coating. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical scheme and advantages of the embodiments of the application clearer, the technical scheme in the embodiments of the application will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the application, not all the embodiments. The components of the embodiments of the application shown can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the application is not intended to limit the scope of the claimed application, but only represents selected embodiments of the application. Based on the embodiments of the application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the application.

[0032] Table 1 Reaction conditions and amounts of each substance for each step of Examples 1 to 4 of the present application

[0033]

[0034]

[0035]

[0036] Comparative Example 1

[0037] The sand-milled slurry was introduced into the coating tank, and the slurry concentration was controlled at 300 g / L (based on TiO2), while the temperature was raised to 80°C. 3.0% NaSiO3 (based on SiO2) was added within 40 minutes, and homogenized for 30 minutes. H3PO4 was added to adjust the pH to 3.0, and the adjustment was performed for 50 minutes, followed by homogenization for 30 minutes. 2.0% ZnCl2 and 3.0% Na2HPO4 solution were simultaneously added within 60 minutes, and homogenized for 20 minutes. H2SO4 was added to adjust the pH to 5.0, and the adjustment was performed for 40 minutes, followed by homogenization for 30 minutes. The temperature was lowered to 40°C. Al2(SO4)3 was added within 40 minutes to adjust the pH to 2.0, and homogenized for 30 minutes. Sodium metaaluminate was added within 40 minutes to adjust the pH to 10.0, and homogenized for 30 minutes. Dilute H2SO4 was used to adjust the pH to 5.5, and the adjustment was performed for 30 minutes, followed by homogenization for 120 minutes. Water washing, flashing, and steam-powdering were performed to obtain the coated titanium dioxide.

[0038] Comparative Example 2

[0039] Fifty-five cubic meters of alkali solution filtrate was collected from the production process of titanium dioxide. After sufficient sedimentation, fifty cubic meters of the upper clear filtrate was taken, and the solid content of the clear filtrate was measured to be 8 ppm, and the concentration of sodium hydroxide was 15.3%. The clear filtrate was added to a mixing tank, and a measured amount of solid sodium hydroxide was added to adjust the concentration of sodium hydroxide in the solution to 33%, obtaining a mixed alkali solution. Twenty cubic meters of the above-mentioned mixed alkali solution (equivalent to 9.0 tons of sodium hydroxide) was added to a sodium metaaluminate preparation tank, and steam heating was started. When the alkali solution was heated to 60°C, a measured amount of aluminum hydroxide powder 4 tons was added at a constant speed under continuous stirring, and the addition was completed within 30 minutes. The heating was continued until the solution boiled, and after the complete dissolution of aluminum hydroxide, the boiling was maintained for 15 minutes. A measured amount of desalted water was added at a constant speed to dilute the sodium metaaluminate solution to an alumina content of Al2O3 = 95 g / l. After sufficient cooling, the sodium metaaluminate solution was obtained. Sixty kilograms of deionized water was weighed, and a sodium silicate solution containing 120 g of SiO2 was added. Under stirring, sixty kilograms of uncoated rutile titanium dioxide was added to prepare a titanium dioxide slurry with a TiO2 content of 800 g / L. The titanium dioxide was sand-milled to achieve the original particle size. The sand-milled titanium dioxide slurry was diluted to a concentration of 300 g / L with deionized water, and then classified by a hydrocyclone,

[0040]

[0041] The qualified overflow slurry is transferred into the coating tank, and the amount is 50 kg in terms of Ti02. In the coating tank, the temperature of the slurry is raised to 50°C by indirect heating with steam. The pH value of the slurry is adjusted to 10.2, and 20 L of the sodium metaaluminate solution obtained in step (4) is added. A 15% concentrated dilute sulfuric acid solution is added to adjust the pH value of the slurry to 6.8. Under the condition that the pH value of the slurry is maintained at 7.0 by using dilute alkali, 2.5 L of an aluminum sulfate solution with an Al203 content of 100 g / L is added, and then the pH value of the slurry is adjusted to 6.8. After the titanium dioxide slurry coated by the above steps is aged for 60 minutes under heat preservation and stirring, it is filtered, washed with water until the resistivity of the filter cake is 252 ohm, and then the filter cake is dried, crushed by an air flow crusher, and the coated titanium dioxide powder is obtained.

[0042] Comparative Example 3

[0043] Different from Example 1, in Comparative Example 3, dilute phosphoric acid and sodium metaaluminate are used for concurrent coating.

[0044] The coated titanium dioxide powders obtained in Examples 1-4 and Comparative Examples 1-3 are subjected to QUVA aging performance test. A UVA (340) lamp is used as a light source, and the sample is placed in an ultraviolet aging machine. The test conditions meet the following requirements: blackboard temperature is (60±2) °C, irradiance is 0.68 W / m2, condensation temperature is (45±2) °C, test cycle period is 8 hours, 4 hours of light / 4 hours of condensation, and continuous ultraviolet light accelerated photoaging is 1000 h. The data in Table 1 below are obtained. 2

[0045] Table 2 Data table of light aging performance index of the titanium dioxide powders obtained in Examples 1-4 and Comparative Examples 1-3 (after aging for 1000 h by an ultraviolet light accelerated aging test machine)

[0046]

[0047] The above examples and comparative examples show that the phosphorus aluminum coating agent prepared by the present application has excellent application performance index in the laminated paper system when used as a titanium dioxide powder for laminated paper. After ultraviolet light accelerated aging for 1000 h, the color difference △E and 60° gloss loss are both better than those of the comparative examples.

[0048] Table 3 Cost saving table of phosphorus aluminum coating agent process relative to existing sodium metaaluminate coating

[0049]

[0050] ​Therefore, the application adopts aluminum hydroxide to react with phosphoric acid to form the soluble salt of aluminum phosphate, which is used as a coating agent for the surface treatment of titanium dioxide, the aluminum phosphate film layer is relatively dense, which can improve the hydrophilic property of the pigment, increase the retention rate in the paper system, and enhance the light resistance of laminated paper. When aluminum or aluminum compounds react with phosphoric acid, short chains among oxygen, phosphorus and aluminum atoms can be formed. By reducing the pH value of the reaction system, the short chains can quickly coagulate into long chains to form a network body, which has high surface affinity and can cover other pigments, thereby improving the light absorption of titanium dioxide. The improvement of light absorption can improve the light resistance, weather resistance and hiding power of titanium dioxide, improve the whiteness and gloss of the product, and prevent discoloration or decomposition under ultraviolet light.

[0051] The above-described embodiments only express the specific implementation of the present application, which is described in detail, but it should not be understood as a limitation on the protection scope of the present application. It should be noted that for ordinary skilled persons in the art, without departing from the technical concept of the present application, a number of modifications and improvements can be made, which are within the protection scope of the present application.

Claims

1. A method for using an aluminum phosphorus coating agent to coat titanium dioxide, characterized in that, Includes the following steps: Step A: A quantitative titanium dioxide slurry is injected into the coating equipment, stirred, and its concentration is measured and adjusted to the qualified range to obtain slurry A; Step B: Add aluminum phosphate coating agent to slurry A, adjust the pH, and after maturation, obtain slurry B with a pH of 6.0-6.5; Step C: Add aluminum phosphate coating agent and sodium aluminate solution to slurry B in parallel flow, and after maturation, obtain slurry C with a pH of 6.0-7.5; Step D: Add sodium aluminate solution to slurry C, and after aging, obtain slurry D with a pH of 8.0-8.5; Step E: Add aluminum sulfate solution and sodium aluminate solution to slurry D in a parallel flow. After aging, slurry E with a pH of 8.0-8.5 is obtained. Step F: Adjust the pH value of slurry E to obtain the coated titanium dioxide slurry; The preparation method of the phosphorus aluminum coating agent includes the following steps: Step 1: Mix phosphoric acid and aluminum hydroxide to obtain compound A; the molar ratio of phosphoric acid to aluminum hydroxide is 3:

1. Step 2: Let mixture A mature for a certain period of time to obtain compound B; Step 3: Add dilution water to mixture B to obtain the aluminum phosphate coating agent.

2. The method for using the aluminum phosphorus coating agent according to claim 1 to coat titanium dioxide, characterized in that, In step 2, the maturation time for mixture A is 55–65 minutes.

3. The method for using the aluminum phosphate coating agent according to claim 1 to coat titanium dioxide, characterized in that, In step 3, add dilution water until the concentration of P2O5 is 100-120 g / L.

4. A method for using an aluminum phosphorus coating agent to coat titanium dioxide according to claim 1, characterized in that, The ratio of the total mass of the phosphorus aluminum coating agent added in steps B and C to the titanium dioxide, calculated as P2O5, is 2.2-3%.

5. A method for using an aluminum phosphate coating agent to coat titanium dioxide according to claim 1, characterized in that, The ratio of the total mass of sodium aluminate and aluminum sulfate added in steps C, D and E to titanium dioxide, calculated as Al2O3, is 5.0 to 6.0%.

6. A method for using an aluminum phosphate coating agent to coat titanium dioxide according to claim 1, characterized in that, The pH value of the coated titanium dioxide slurry obtained in step F is 5.5 to 6.0.

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