Preparation method of titanium dioxide for high-coverage and high-light-fastness laminated paper

Abstract

The present invention discloses a preparation method of titanium dioxide for high-covering and high-lightfast laminated paper, comprising the following steps: S1. Take the initial product of titanium dioxide to prepare a titanium dioxide-based material slurry; S2. Adjust the pH of the slurry to 8-12, and at the same time add a magnesium source, a silicic acid source and a pH regulator, and maintain the countercurrent pH at 8-12 to homogenize and form a magnesium silicate film layer; S3. Adjust the pH of the slurry to 5-6, and at the same time add an aluminum source and a phosphoric acid source, and maintain the countercurrent pH at 5-6 to homogenize and form an aluminum phosphate film layer after homogenization; S4. Add a first aluminum source to adjust the pH to 11-13 and homogenize; then add a second aluminum source to adjust the pH to 3-5 and homogenize; finally add a third aluminum source to adjust the pH to 6.5-7.5 and homogenize to form a polycrystalline composite alumina film layer. The product obtained in this application has a uniform and dense film layer and high retention rate, lightfastness and covering power, making it can be well applied to laminated paper.

Description

Technical Field

[0001] The present invention belongs to the technical field of titanium dioxide preparation, and specifically relates to a preparation method of titanium dioxide for high-coverage and high-light-fast laminated paper. Background Art

[0002] Titanium dioxide has non-toxicity, excellent whiteness, coloring power, covering power, weather resistance, heat resistance and chemical stability, and is considered to be the best-performing white pigment in the world at present. It is widely used in industries such as coatings, plastics, papermaking, printing inks, chemical fibers, rubber, and cosmetics.

[0003] The papermaking industry is the third largest user of titanium dioxide. As a paper filler, it is mainly used in high-grade papers and thin papers. The requirements for decorative laminated paper include covering power, light fastness, color fastness, wet strength, impregnation adaptability and printability. The main component of titanium dioxide, TiO 2 belongs to N-type semiconductor oxides and has photocatalytic activity. After being irradiated by light and heated, the peripheral electrons are excited to generate photogenerated electrons and photogenerated holes. Under anoxic conditions, the photogenerated electrons reduce TiO 2 to generate Ti 2 O 3 , which makes the melamine laminated paper turn gray, seriously affecting the various properties and service life of the decorative paper. Therefore, titanium dioxide pigments used in laminated paper often need to be specially surface-treated to meet the requirements of light fastness and heat resistance. Currently, the most common coatings for titanium dioxide used in laminated paper are some compounds of cerium, zirconium, silicon, phosphorus, aluminum, and magnesium.

[0004] The main factors affecting the covering power of titanium dioxide are: rutile content, particle size, particle size distribution, particle structure, and dispersion degree; taking architectural latex paint as an example, performing a heavy coating treatment on titanium dioxide pigments to increase the surface porosity of titanium dioxide pigments to improve the covering power performance of titanium dioxide pigments in latex paint has become a widespread technology. Similarly, this method can also be used in papermaking to improve the covering power of titanium dioxide used in papermaking. Patent CN106497147B discloses a method of respectively coating a dense hydrated amorphous silica film, a loose porous film mainly composed of hydrated aluminum silicate, and a loose hydrated alumina film on the surface of titanium dioxide particles. The titanium dioxide pigment prepared by this method is particularly suitable for fields with high dry covering power requirements; Patent CN111393876B improves the covering power by introducing a small molecule template agent during the coating process and removing it by calcination to obtain a porous film layer.

[0005] To improve light resistance, methods such as adding light stabilizers and antioxidants are often used. Antioxidants, also known as anti-aging agents, are divided into two categories: phenolic and phosphate ester types. According to different action mechanisms, antioxidants can be roughly divided into the following three categories: (1) Free radical absorbers: such as phenolic antioxidants, vitamin E, and carotenoids; (2) Oxygen scavengers: such as carotenoids and their derivatives, ascorbic acid, ascorbyl palmitate, erythorbic acid, and sodium erythorbate, etc.; (3) Metal ion chelating agents: citric acid, EDTA, and phosphate derivatives.

[0006] Patent CN101857736A discloses a method for improving the light resistance of titanium dioxide by coating with zirconium, phosphorus, and aluminum. However, this method uses expensive zirconium raw materials and has limited improvement in light resistance. Patent US4461810 discloses a method for improving the light resistance of titanium dioxide. During the post-treatment process of titanium dioxide, a cerium salt is added. Utilizing the principle that the redox potential of Ce 4+ / Ce 3+ is higher than that of Ti 4+ / Ti 3+ and ensuring the light resistance of titanium dioxide when Ce 4+ is present, Ti 4+ will not be reduced. However, the introduction of the cerium salt may cause the hue of titanium dioxide to be yellowish and increase production costs. Patent CN1132769A discloses a method of respectively precipitating a layer of aluminum phosphate oxide, a layer of alumina precipitate, and a layer of magnesium oxide on the surface of titanium dioxide, and improving the retention rate of titanium dioxide in pulp by depositing magnesium oxide on the surface of titanium dioxide. Chinese Patent CN104179066B coats a silicon-containing compound and an aluminum-containing compound on the surface of titanium dioxide, and then performs processes such as calcination to remove the hydroxyl groups on the coating film, avoiding the reaction of electron pairs and meeting the requirements of high light resistance of titanium dioxide in the field of decorative laminated paper.

[0007] Currently, the retention rate of titanium dioxide used in laminated paper in pulp is low, the dispersion performance and hiding power are poor, and the light resistance is not good, resulting in poor light fastness of decorative laminated paper. Therefore, there is an urgent need to develop a titanium dioxide with high retention rate, good hiding power, and light resistance. Summary of the Invention

[0008] The purpose of the present invention is to provide a preparation method of titanium dioxide for high-hiding and high-light-resistant laminated paper to solve the deficiencies of the prior art.

[0009] The purpose of the present invention is achieved by the following technical solutions:

[0010] A preparation method of titanium dioxide for high-hiding and high-light-resistant laminated paper includes the following steps:

[0011] S1. Take the titanium dioxide crude product, add a dispersant for pulping and sanding to prepare a titanium dioxide-based material slurry; the dispersant is citric acid or a citric acid derivative;

[0012] S2. Adjust the pH of the slurry to 8 - 12, and at the same time add a magnesium source, a silicon source, and a pH regulator, and maintain the co-current pH at 8 - 12 to homogenize and form a magnesium silicate film layer;

[0013] S3. Adjust the pH of the slurry to 5 - 6, and at the same time add an aluminum source and a phosphorus source, and maintain the co-current pH at 5 - 6 to homogenize and form an aluminum phosphate film layer after homogenization;

[0014] S4. Add a first aluminum source to adjust the pH to 11 - 13 for homogenization; then add a second aluminum source to adjust the pH to 3 - 5 for homogenization; finally add a third aluminum source to adjust the pH to 6.5 - 7.5 to form a polycrystalline composite alumina film layer after homogenization.

[0015] Preferably, the dosage of the dispersant in step S1 is 0.1 - 1.0% of the total mass of the titanium dioxide crude product in terms of citric acid.

[0016] Preferably, the concentration of the titanium dioxide-based material slurry obtained after sanding in step S1 is 500 - 1000 g / L in terms of titanium dioxide, and the slurry concentration is first diluted to 250 - 350 g / L before adjusting the pH in step S2.

[0017] Preferably, the magnesium source in step S2 is one or a combination of two or more of magnesium chloride, magnesium nitrate, and magnesium sulfate, and the addition amount is 1 - 2% of the mass of the titanium dioxide substrate in terms of MgO; the silicon source is at least one of sodium silicate and potassium silicate, and the addition amount is 2.0 - 4.0% of the mass of the titanium dioxide substrate in terms of silicon dioxide.

[0018] Preferably, the co-current addition time of the magnesium source, the silicon source, and the pH regulator in step S2 is 40 - 120 min, and the homogenization time is 20 - 40 min.

[0019] Preferably, the phosphorus source in step S3 is phosphoric acid, and the addition amount is 2 - 3% of the mass of the titanium dioxide substrate in terms of P 2 O 5 calculated as, and the aluminum source is at least one of sodium metaaluminate and potassium metaaluminate, and the addition amount is based on maintaining the slurry pH at 5 - 6.

[0020] Preferably, the co-current addition time of the aluminum source and the phosphorus source in step S3 is 30 - 90 min, and the homogenization time is 20 - 40 min.

[0021] Preferably, the first aluminum source in step S4 is at least one of sodium metaaluminate and potassium metaaluminate, and the addition amount is 1.0 - 1.5% of the mass of the titanium dioxide substrate calculated as alumina, the addition time is 60 - 180 min, the homogenization time is 30 - 90 min, and the pH after homogenization is maintained at 11.0 - 13.0.

[0022] Preferably, the second aluminum source in step S4 is at least one of aluminum sulfate and aluminum chloride, and the addition amount is 1.0 - 1.5% of the mass of the titanium dioxide substrate calculated as alumina, the addition time is 40 - 120 min, the homogenization time is 40 - 120 min, and the pH after homogenization is maintained at 3.0 - 5.0.

[0023] Preferably, the third aluminum source in step S4 is at least one of sodium metaaluminate and potassium metaaluminate, and the addition amount is to adjust the pH of the slurry to 6.5 - 7.5.

[0024] In this application, through the dispersion and induction of citric acid during the magnesium silicate coating process, the obtained product has a uniform and dense film layer and a high retention rate. Through further coating with aluminum phosphate, the purpose of improving light resistance is achieved. Combining with the laminated aluminum film layer coating, the purpose of improving the hiding power of titanium dioxide is achieved, making it suitable for good application in laminated paper. Detailed implementation manners

[0025] The present invention provides a preparation method of titanium dioxide for high - hiding and high - light - resistant laminated paper, including the following steps:

[0026] S1. Take the initial product of titanium dioxide, add a dispersant for pulping and sanding to prepare a titanium dioxide - based material slurry; the dispersant is citric acid or a citric acid derivative;

[0027] S2. Adjust the pH of the slurry to 8 - 12, and at the same time add a magnesium source, a silicic acid source and a pH regulator, and maintain the counter - current pH at 8 - 12 to homogenize and form a magnesium silicate film layer;

[0028] S3. Adjust the pH of the slurry to 5 - 6, and at the same time add an aluminum source and a phosphoric acid source, and maintain the counter - current pH at 5 - 6 to homogenize and form an aluminum phosphate film layer after homogenization;

[0029] S4. Add the first aluminum source to adjust the pH to 11 - 13 and homogenize; then add the second aluminum source to adjust the pH to 3 - 5 and homogenize; finally add the third aluminum source to adjust the pH to 6.5 - 7.5 and homogenize to form a polymorphic composite alumina film layer.

[0030] In this application, a citric acid - based dispersant is first added in the wet - grinding pulping stage. Besides playing a good dispersion role, during the subsequent process of coating magnesium silicate, citric acid reacts with Mg 2+The formation of complex salts delays the reaction with the silicate source, causing magnesium silicate to precipitate slowly and evenly on the surface of titanium dioxide particles, improving the density and uniformity of the film layer. At the same time, magnesium silicate is white, which improves the light resistance of the product without affecting the hue.

[0031] Secondly, paper fibers are negatively charged, and the surface of titanium dioxide is coated with magnesium salts with a higher isoelectric point than alumina (isoelectric point is around 11), and the retention rate of titanium dioxide in paper pulp is improved by precipitating magnesium on the surface of titanium dioxide. At the same time, the effective combination of dense silicon and magnesium not only improves the light resistance of titanium dioxide, but also effectively improves the retention rate of titanium dioxide in paper pulp.

[0032] Aluminum phosphate is coated on the surface of magnesium silicate, and titanium dioxide is exposed to sunlight or ultraviolet light. 2 Produced Ti 3+ , in an oxygen-deficient environment, Ti 3+ Seized PO 4 3- The oxygen in the aluminum phosphate is reduced to aluminum phosphite. The reaction formula is as follows:

[0033] Ti 2 O 3 +PO 4 3- →2TiO 2 +PO 3 3- , since aluminum phosphite is white or transparent, it is not suitable for TiO 2 The whiteness is little affected. When a large amount of PO is produced 3 3- When 3 3- When combined with TiO 2 OH· produced by photochemical reaction combines to form HPO 4 2- , the reaction formula is as follows: PO 3 3- +OH →HPO 4 2- , thus preventing the chemically active OH· from flowing into the TiO 2 In the surrounding organic matrix, it prevents the organic matrix from oxidative degradation and improves the light resistance of titanium dioxide. When aluminum or aluminum compounds react with phosphoric acid, short chains of OPO-Al-OP are formed in the solution, and these short chains condense with each other to form a network of aluminum phosphate film structures, which have high surface affinity for pigments and dense film layers, which can greatly improve the light resistance of the product.

[0034] Furthermore, the present application adopts a laminated new method for aluminizing, enabling the aluminum film layer to precipitate on the surface of titanium dioxide layer by layer. The aluminum is added in a co-current manner, and the pH of the slurry is gradually changed. During the gradual change of pH, by slowly adding the first basic aluminum salt, the pH of the system gradually increases from 5.0 - 6.0 to 11.0 - 13.0. During the gradual increase of pH, the crystal form gradually becomes complete, and various crystal structure aluminums such as AlOOH (boehmite, monohydroxyaluminum oxide), Al(OH) 3 (gibbsite, trihydroxyaluminum oxide), etc. are formed in sequence. 2 O 3 Similarly, during the second coating process, an acidic aluminum salt is added, and the pH is gradually re-adjusted from 11.0 - 13.0 to 3.0 - 5.0. During the gradual decrease of pH, Al(OH) 3 (gibbsite, trihydroxyaluminum oxide), AlOOH (boehmite, monohydroxyaluminum oxide), amorphous Al 2 O 3 mixed film layers are formed in sequence. Furthermore, a reticular and spongy irregular film layer can be obtained. While the compactness and dispersibility are significantly improved, due to the gaps between particles, the opacity and hiding power of the product are also significantly improved. By adding aluminum salt for the third time, the pH of the slurry is adjusted to facilitate water washing of the slurry. The coating of the mixed crystal form of the aluminum film layer not only ensures that amorphous aluminum can adsorb on titanium dioxide but also meets the weather resistance and dispersion performance of the dense film.

[0035] Therefore, through the dispersion and induction effects of citric acid during the magnesium silicate coating process, the product obtained has a uniform and dense film layer and a high retention rate. By further coating with aluminum phosphate, the purpose of improving light resistance is achieved. Combined with the laminated aluminum film layer coating, the purpose of improving the hiding power of titanium dioxide is achieved, making it applicable to laminated paper well.

[0036] Preferably, the dosage of the dispersant in step S1 is 0.1 - 1.0% of the total mass of the initial titanium dioxide product in terms of citric acid.

[0037] Preferably, the concentration of the titanium dioxide-based material slurry obtained after sand grinding in step S1 is 500 - 1000 g / L in terms of titanium dioxide. Before adjusting the pH in step S2, the slurry concentration is first diluted to 250 - 350 g / L.

[0038] Preferably, the coatings in steps S2 and S3 are carried out at 80 - 95 °C. High temperature is beneficial to the coating of magnesium silicate and aluminum phosphate. The coating in step S4 is carried out at 40 - 60 °C. Specifically:

[0039] During the magnesium silicate coating process, the higher the temperature, the more Si(OH) 4The higher the supersaturation, the easier it is to generate polysilicic acid. During the aluminum phosphate coating process, adjusting the reaction temperature can, on the one hand, change the Brownian motion rate of primary aluminum phosphate particles and titanium dioxide particles in the suspension, adjust the probability of collision and adsorption between the two to form a film, and thus control the uniformity of the coating layer. On the other hand, it can adjust the hydrolysis rate of the phosphorus source, control the concentration of primary aluminum phosphate particles generated in the reaction in the suspension, and thus control the degree of agglomeration of the coating layer. Magnesium silicate and aluminum phosphate can form a continuous and dense film layer at a higher temperature, preventing water molecules from passing through and enhancing its weather and light resistance performance.

[0040] In the alumina coating process, if the temperature is high, the crystal form is more prominent and there are more self-nucleations; if the temperature is low, the crystal form is not so prominent and the coating will be more complete, and the light retention rate and hue of the product will be better. At the same time, if high-temperature deposition occurs, boehmite crystals are likely to appear, which will deteriorate the pigment performance. Therefore, under high pH conditions, the temperature needs to be reduced to form pseudo-boehmite alumina and improve the dispersibility.

[0041] Preferably, in step S2, the magnesium source is one or more combinations of magnesium chloride, magnesium nitrate, and magnesium sulfate, and the addition amount is 1-2% of the mass of the titanium dioxide substrate in terms of MgO. It is preferably added in the form of a solution, and the solution concentration is 80-200 g / L in terms of MgO; the silicate source is at least one of sodium silicate and potassium silicate, and the addition amount is 2.0-4.0% of the mass of the titanium dioxide substrate in terms of silicon dioxide. It is preferably added in the form of a solution, and the solution concentration is 80-200 g / L in terms of SiO 2 2. The method according to claim 1, wherein the pH regulator is an alkali solution (such as one or both of sodium hydroxide and potassium hydroxide solutions, preferably NaOH, with a concentration of 160 g / L) or an acid solution (such as one or both of sulfuric acid and hydrochloric acid, preferably sulfuric acid, with a concentration of 100-200 g / L).

[0042] Preferably, in step S2, the co-current addition time of the magnesium source, silicate source, and pH regulator is 40-120 min, and the homogenization time is 20-40 min.

[0043] Preferably, in step S3, the phosphorus source is phosphoric acid, and the addition amount is 2-3% of the mass of the titanium dioxide substrate in terms of P 2 2 5 5; the aluminum source is at least one of sodium metaaluminate and potassium metaaluminate, and the addition amount is to maintain the pH of the slurry at 5-6. It is preferably added in the form of a solution, and the solution concentration is 80-200 g / L in terms of Al 2 2 3 3.

[0044] Preferably, in step S3, the co-current addition time of the aluminum source and phosphorus source is 30-90 min, and the homogenization time is 20-40 min.

[0045] Preferably, in step S4, the first aluminum source is an alkaline aluminum source, specifically at least one of sodium metaaluminate and potassium metaaluminate. The addition amount is 1.0-1.5% of the mass of the titanium dioxide substrate calculated as alumina, the addition time is 60-180 min, the homogenization time is 30-90 min, and the pH after homogenization is maintained at 11.0-13.0.

[0046] Preferably, in step S4, the second aluminum source is an acidic aluminum source, at least one of aluminum sulfate and aluminum chloride. The addition amount is 1.0-1.5% of the mass of the titanium dioxide substrate calculated as alumina. It is preferably added in the form of a solution, and the solution concentration is 80-200 g / L calculated as Al 2 O 3 The addition time is 40-120 min, the homogenization time is 40-120 min, and the pH after homogenization is maintained at 3.0-5.0.

[0047] Preferably, in step S4, the third aluminum source is an alkaline aluminum source, at least one of sodium metaaluminate and potassium metaaluminate. Taking NaAlO 2 as the preference, the addition amount is based on adjusting the pH of the slurry to 6.5-7.5. It is preferably added in the form of a solution, and the solution concentration is 80-150 g / L calculated as Al 2 O 3 The adjustment time is 30-60 min, and then it is homogenized for 60-180 min. After the homogenization is completed, if the pH value is not within the range of 6.5-7.5, it is finely adjusted with an acidic aluminum source or an alkaline aluminum source. After homogenization, the slurry is washed, flash evaporated, and steam pulverized to obtain a titanium dioxide product.

[0048] In the present invention, operations such as washing, flash evaporation, and steam pulverization are all carried out in a conventional manner in the art.

[0049] Example 1

[0050] Prepare qualified sanded slurry and pump it into the coating tank. Adjust the slurry concentration to 300 g / L (calculated as TiO 2 ), and at the same time heat it up to 80 °C; adjust the pH to 8.0 with NaOH, and add 1.0% MgSO 4 and 2% Na 2 SiO 3 in parallel flow within 60 min, keep the pH = 8.0, and homogenize for 30 min; add H 3 PO 4 (calculated as P 2 O 5 ) to adjust the pH to 5.0 within 20 min and homogenize for 20 min; add 2.0% H 3 PO 4 and NaAlO 2 in parallel flow within 60 min. Here, NaAlO 2The addition amount is based on maintaining the pH at 5.0. Keep the pH = 5.0 and homogenize for 30 min; cool the slurry to 50 °C and add 1.0% NaAlO 2 , homogenize for 30 min, and control the pH at 11.2 after homogenization; add 1.0% Al 2 (SO 4 ) 3 (calculated as Al 2 O 3 ) within 60 min, homogenize for 40 min, and control the pH at 4.8 after homogenization; adjust the final pH to 6.6 with NaAlO 2 , adjust for 30 min, homogenize for 60 min, and maintain the pH at 6.6 after homogenization. If the pH value is not within this range, fine-tune with aluminum sulfate or sodium aluminate, then perform water washing, flash evaporation, and steam powdering to obtain the finished product.

[0051] Example 2

[0052] Prepare qualified sanding slurry and pump it into the coating tank. Adjust the slurry concentration to 300 g / L (calculated as TiO 2 ), and at the same time heat up to 85 °C; adjust the pH to 8.5 with NaOH and add 1.5% MgSO 4 and 3.5% Na 2 SiO 3 in parallel within 90 min, keep the pH = 8.5, and homogenize for 30 min; add H 3 PO 4 (calculated as P 2 O 5 ) within 20 min to adjust the pH to 5.5 and homogenize for 20 min; add 2.5% H 3 PO 4 and NaAlO 2 in parallel within 60 min. Here, the addition amount of NaAlO 2 is based on maintaining the pH at 5.5. Keep the pH = 5.5 and homogenize for 30 min; cool the slurry to 55 °C and add 1.2% NaAlO 2 within 90 min, homogenize for 30 min, and control the pH at 12.0 after homogenization; add 1.2% Al 2 (SO 4 ) 3 (calculated as Al 2 O 3 ) within 90 min, homogenize for 40 min, and control the pH at 4.0 after homogenization; adjust with NaAlO 2Adjust the final pH to 6.7, with an adjustment time of 30 min, homogenize for 60 min, and maintain the pH at 6.7 after homogenization. If the pH value is not within this range, fine-tune it with aluminum sulfate or sodium meta-aluminate, and then perform water washing, flash evaporation, and steam pulverization to obtain the finished product.

[0053] Example 3

[0054] Prepare qualified sanding abrasive slurry and pump it into the coating tank, adjust the slurry concentration to 300 g / L (calculated based on TiO 2 ), and at the same time heat up to 90 °C; adjust the pH to 9.0 with NaOH, and add 1.8% MgSO 4 and 4.0% Na 2 SiO 3 in parallel flow within 120 min, maintain the pH = 9.0, and homogenize for 30 min; add H 3 PO 4 (calculated based on P 2 O 5 ) to adjust the pH to 6.0 within 20 min, and homogenize for 20 min; add 3.0% H 3 PO 4 and NaAlO 2 in parallel flow within 90 min, where the addition amount of NaAlO 2 is based on maintaining the pH at 6.0, maintain the pH = 6.0, and homogenize for 30 min; cool the slurry to 60 °C, add 1.5% NaAlO 2 within 120 min, and homogenize for 30 min. After homogenization, control the pH at 12.5; add 1.5% Al 2 (SO 4 ) 3 (calculated based on Al 2 O 3 ) within 90 min, and homogenize for 40 min. After homogenization, control the pH at 3.5; adjust the final pH to 6.8 with NaAlO 2 , with an adjustment time of 30 min, homogenize for 60 min, and maintain the pH at 6.8 after homogenization. If the pH value is not within this range, fine-tune it with aluminum sulfate or sodium meta-aluminate, and then perform water washing, flash evaporation, and steam pulverization to obtain the finished product.

[0055] Comparative Example 1

[0056] Coating is carried out using conventional dense silicon, aluminum phosphate, and boehmite alumina. Among them, the dense silicon coating is 3.0%, the aluminum phosphate coating is 3.0%, and the aluminum coating is 4.0%. The method is as follows: Prepare qualified sanded slurry and introduce it into the coating tank, add water to dilute the concentration to 300 g / L, heat the slurry to 85 °C, adjust the pH of the slurry to 10.4, add 3.0% sodium silicate, slowly add sulfuric acid to adjust the pH to 7.0, and the sulfuric acid adjustment time is 180 min; adjust the pH of the slurry to 5.0, and add 3.0% H 3 PO 4 and Y1% NaAlO 2 (where Y1 is based on adjusting the pH of the slurry to 5.0), control the pH of the slurry to 5.0, and homogenize for 30 min; then use Y2 NaAlO 2 (where Y2 is based on adjusting the pH of the slurry to 8.0) to adjust the pH to 8.0, and add (4.0 - Y1 - Y2) NaAlO 2 and Al 2 (SO 4 ) 3 in parallel flow within 120 min and control the pH to 8.0 (where NaAlO 2 / Al 2 (SO 4 ) 3 = 1.25, and both NaAlO 2 and Al 2 (SO 4 ) 3 are calculated based on Al 2 O 3 ), and homogenize for 30 min; adjust the end pH of H 2 SO 4 to 6.6, and then perform water washing, flash evaporation, and steam pulverization to obtain the finished product.

[0057] Comparative Example 2

[0058] Coating is carried out using conventional dense silicon, aluminum phosphate, and mixed crystal alumina composite coating. Among them, the dense silicon coating is 3.0%, the aluminum phosphate coating is 3.0%, and the aluminum coating is 4.0%. The method is as follows: Prepare qualified sanded slurry and introduce it into the coating tank, add water to dilute the concentration to 300 g / L, heat the slurry to 85 °C, adjust the pH of the slurry to 10.4, add 3.0% sodium silicate, slowly add sulfuric acid to adjust the pH to 7.0, and the sulfuric acid adjustment time is 180 min; adjust the pH of the slurry to 5.0, and add 3.0% H 3 PO 4 and NaAlO 2 (the addition amount of sodium metaaluminate is based on adjusting the pH of the slurry to 5.0), control the pH of the slurry to 5.0, and homogenize for 30 min;

[0059] The mixed crystal alumina coating is the same as in Example 3 (in this example, the total addition amount of all aluminum sources is about 4.0%).

[0060] Comparative Example 3

[0061] Conventional aluminum phosphate, alumina, and magnesium oxide composite coating is used. Among them, the aluminum phosphate coating is 3.0%, the aluminum coating is 4.0%, and the magnesium oxide is 0.8%. The method is as follows: Prepare a qualified sanding slurry and introduce it into the coating tank, add water to dilute the concentration to 300 g / L, heat the slurry to 85 °C, adjust the pH of the slurry to 5.0, and add 3.0% H 3 PO 4 and Y1% NaAlO 2 (Y1 is based on adjusting the pH of the slurry to 5.0), control the pH of the slurry to 5.0, and homogenize for 30 min; Y2 NaAlO 2 (Y2 is based on adjusting the pH of the slurry to 8.0) adjust the pH to 8.0, and add (4.0 - Y1 - Y2) NaAlO in parallel flow within 120 min 2 and Al 2 (SO 4 ) 3 and control the pH to 8.0 (where NaAlO 2 / Al 2 (SO 4 ) 3 = 1.25, NaAlO 2 and Al 2 (SO 4 ) 3 are both calculated based on Al 2 O 3 ), homogenize for 30 min; adjust the pH to 8.5, add 0.8% MgSO 4 and a pH regulator in parallel flow within 40 min, and control the pH to 8.5, homogenize for 30 min; H 2 SO 4 adjust the end point pH to 6.6, and then perform water washing, flash evaporation, and steam powdering to obtain the finished product.

[0062] Comparative Example 4

[0063] Coating with citric acid, magnesium silicate, and mixed crystal alumina, see Example 3 for details, but omit the aluminum phosphate coating step.

[0064] Application test comparison

[0065] The titanium dioxide prepared in Examples 1 - 3 and Comparative Examples 1 - 4 was subjected to paper-making application performance testing. The specific testing method used the conventional method in the field. The results are shown in Tables 1 - 2:

[0066] 1. Comparison of titanium dioxide retention and hiding power

[0067] Table 1

[0068] Sample Retention rate Hiding power Example 1 82.0 90.85 Example 2 83.6 91.73 Example 3 85.4 92.34 Comparative Example 1 80.9 90.33 Comparative Example 2 81.3 90.92 Comparative Example 3 81.8 90.27 Comparative Example 4 81.4 90.65

[0069] 2. Lightfastness evaluation

[0070] Table 2 Xenon lamp aging results

[0071] Sample Lightfastness ΔE Example 1 1.38 Example 2 1.20 Example 3 0.92 Comparative Example 1 1.46 Comparative Example 2 1.43 Comparative Example 3 1.50 Comparative Example 4 1.55

[0072] From the above data, it can be seen that the titanium dioxide prepared by the present invention has good advantages in terms of retention, covering power and lightfastness.

[0073] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the appended claims are intended to be construed as including the preferred embodiments and all changes and modifications falling within the scope of the present invention. Obviously, those skilled in the art can make various changes and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A preparation method of titanium dioxide for high-covering and high-lightfast laminated paper, characterized in that, it comprises the following steps: S1. Take the initial product of titanium dioxide, add a dispersant and carry out beating and sanding to prepare a titanium dioxide-based material slurry; the dispersant is citric acid or a citric acid derivative; S2. Adjust the pH of the slurry to 8-12, and at the same time add a magnesium source, a silica source and a pH regulator, and maintain the concurrent-flow pH at 8-12 to homogenize and form a magnesium silicate film layer; the addition amount of the magnesium source is calculated as MgO and is 1-2% of the mass of the titanium dioxide base material; the addition amount of the silica source, calculated as silicon dioxide, is 2.0-4.0% of the mass of the titanium dioxide base material; S3. Adjust the pH of the slurry to 5-6, and simultaneously add an aluminum source and a phosphorus source, maintain the pH of the co-current flow at 5-6, and form an aluminum phosphate film layer after homogenization; the addition amount of the phosphorus source is calculated based on P 2 O 5 and is 2-3% of the mass of the titanium dioxide substrate; S4. Add the first aluminum source to adjust the pH to 11-13 and homogenize; then add the second aluminum source to adjust the pH to 3-5 and homogenize; finally add the third aluminum source to adjust the pH to 6.5-7.5, and form a polycrystalline composite alumina film layer after homogenization; the addition amount of the first aluminum source is calculated as alumina and is 1.0-1.5% of the mass of the titanium dioxide base material; the addition amount of the second aluminum source is calculated as alumina and is 1.0-1.5% of the mass of the titanium dioxide base material; The coating in step S4 is carried out at 40-60°C.

2. The preparation method of titanium dioxide for high-covering and high-lightfast laminated paper according to claim 1, characterized in that, the dosage of the dispersant in step S1 is 0.1-1.0% of the total mass of the initial product of titanium dioxide calculated as citric acid.

3. The preparation method of titanium dioxide for high-covering and high-lightfast laminated paper according to claim 1, characterized in that, the concentration of the titanium dioxide-based material slurry obtained after sanding in step S1 is 500-1000 g / L calculated as titanium dioxide, and the slurry concentration is first diluted to 250-350 g / L before adjusting the pH in step S2.

4. The preparation method of titanium dioxide for high-covering and high-lightfast laminated paper according to claim 1, characterized in that, the magnesium source in step S2 is one or a combination of two or more of magnesium chloride, magnesium nitrate, and magnesium sulfate; the silica source is at least one of sodium silicate and potassium silicate.

5. The preparation method of titanium dioxide for high-covering and high-lightfast laminated paper according to claim 1, characterized in that, the concurrent-flow addition time of the magnesium source, the silica source and the pH regulator in step S2 is 40-120 min, and the homogenization time is 20-40 min.

6. The preparation method of titanium dioxide for high-covering and high-lightfast laminated paper according to claim 1, characterized in that, the phosphoric acid source in step S3 is phosphoric acid, the aluminum source is at least one of sodium metaaluminate and potassium metaaluminate, and the addition amount is to maintain the pH of the slurry at 5-6.

7. The preparation method of titanium dioxide for high-covering and high-lightfast laminated paper according to claim 1, characterized in that, the concurrent-flow addition time of the aluminum source and the phosphoric acid source in step S3 is 30-90 min, and the homogenization time is 20-40 min.

8. The preparation method of titanium dioxide for high-covering and high-lightfast laminated paper according to claim 1, characterized in that, The first aluminum source described in step S4 is at least one of sodium aluminate and potassium aluminate, the addition time is 60 to 180 minutes, the homogenization time is 30 to 90 minutes, and the pH after homogenization is maintained at 11.0 to 13.

0.

9. The method for preparing titanium dioxide for high-opacity and high-light-fastness laminated paper as described in claim 1, characterized in that, the second aluminum source described in step S4 is at least one of aluminum sulfate and aluminum chloride, the addition time is 40 to 120 minutes, the homogenization time is 40 to 120 minutes, and the pH after homogenization is maintained at 3.0 to 5.

0.

10. The method for preparing titanium dioxide for high-opacity and high-light-fastness laminated paper as described in claim 1, characterized in that, the third aluminum source described in step S4 is at least one of sodium aluminate and potassium aluminate, and the addition amount is based on adjusting the pH of the slurry to 6.5 to 7.5.