Preparation method for titanium dioxide pigment for recycled polyolefin and prepared titanium dioxide powder

Abstract

The present application relates to the technical field of titanium dioxide preparation methods. Specifically disclosed are a preparation method for a titanium dioxide pigment for recycled polyolefin and a prepared titanium dioxide powder. The preparation method comprises: by means of using rutile titanium dioxide having a concentration of 20-24 wt% and a particle size of 0.15-0.25 μm as a raw material, coating same with a silicon oxide film layer at 70-85℃, coating same with a zirconium oxide film layer at 60-70℃, and then separately coating same with an aluminum phosphate film layer and a boehmite-type aluminum oxide film layer at 50-65℃; and performing filtration, washing, dehydration, drying and airflow pulverization, and then performing organic coating treatment. The present preparation method uses a slurry having a low titanium dioxide concentration as a raw material, involves different coating temperatures, and limits the types of the coating layers, so that the obtained product exhibits oxidation degradation resistance, low yellowing and excellent weather fastness in recycled polyolefin plastic systems, and also exhibits excellent compatibility, dispersibility and processing fluidity.

Description

Preparation method of titanium dioxide pigment for recycled polyolefin and prepared titanium white powder TECHNICAL FIELD

[0001] The application relates to the technical field of a titanium dioxide preparation method, and more particularly to a preparation method of a titanium dioxide pigment for recycled polyolefin and a prepared titanium white powder. BACKGROUND

[0002] Recycled plastic refers to plastic raw materials obtained by processing and treating waste plastic through physical or chemical methods such as pretreatment (screening, classification, cleaning), melt granulation and modification, and is a recycling of plastic. According to the material characteristics, the recycled plastic is mainly PP, PE and other thermoplastic polyolefin products, and the two are also the most common plastic packaging film materials.

[0003] In order to improve the heat resistance, light resistance and weather resistance of recycled plastic products, such as yellowing of polyolefin and other resins, and improve the service life, titanium dioxide pigment (also known as titanium white powder) needs to be added, which can also effectively optimize the mechanical properties and electrical properties of the plastic product.

[0004] However, it is found that the use of the following currently marketed titanium dioxide products mixed with PP resin for panel detection has the following problems: the use of general rutile titanium dioxide has poor temperature resistance, and the yellowing index is as high as 3.15; the use of general rutile titanium dioxide for plastics has a yellowish color phase and a low whiteness of 93.78; and the use of anatase titanium dioxide has poor weather resistance and light stability ΔΕ as high as 2.56, and the stability is insufficient, which cannot meet the use needs. SUMMARY

[0005] In order to improve the whiteness of the titanium dioxide pigment in the polyolefin resin system, reduce the yellowing and improve the weather resistance, the application provides a preparation method of a titanium dioxide pigment for recycled polyolefin and a prepared titanium white powder.

[0006] In a first aspect, the application provides a preparation method of a titanium dioxide pigment for recycled polyolefin, which adopts the following technical scheme:

[0007] A preparation method of a titanium dioxide pigment for recycled polyolefin, comprising the following steps:

[0008] S1, using rutile titanium dioxide primary slurry with a concentration of 20-24wt% and a particle size of 0.15-0.25μm as raw material, coating a silicon oxide film layer at 70-85℃, coating a zirconium oxide film layer at 60-70℃, and then respectively coating an aluminum phosphate film layer and a boehmite type aluminum oxide film layer at 50-65℃;

[0009] S2, after filtration, washing, dewatering and drying, and airflow crushing, organic film coating treatment is performed, and the titanium dioxide pigment for recycled polyolefin is obtained.

[0010] By adopting the technical scheme, S1 adopts a low-titanium dioxide concentration slurry as raw material, different coating temperatures, a special coating formula combination, and limits the type of coating layer, so that the obtained product has the properties of anti-oxidation degradation, yellowing and better weather resistance in the regenerated polyolefin plastic system. Among them, (1) a low-content amorphous silicon dioxide film layer is coated first to block the lattice defects and shield the surface light active points, improve the anti-oxidation and anti-ultraviolet properties, and the higher temperature of 70-85℃ is limited for coating, and the slower PH value adjustment deposition rate makes the silicon dioxide film layer more dense; (2) a small amount of zirconium dioxide film layer is coated to enhance the weather resistance and improve the brightness of the product, and the higher temperature of 60-70℃ is limited for coating, and the slower flow rate maintains the PH value deposition rate, so that the zirconium dioxide film layer is dense; (3) an aluminum phosphate film is coated to improve the light resistance and anti-yellowing properties of titanium dioxide, the coating agent is added at one time, and the sodium aluminate and aluminum sulfate are synchronously and slowly adjusted in PH value deposition rate; (4) a lower content of boehmite type aluminum oxide is coated to enhance the gloss and improve the dispersibility of the product; the lower temperature of 50-60℃ is limited for coating, and the sodium aluminate and aluminum sulfate are directly synchronously and slowly adjusted in PH value deposition rate.

[0011] S2 adopts organic coating treatment to enhance the compatibility, dispersibility and processing fluidity of the product in the polyolefin plastic system, and finally obtains a titanium dioxide pigment product that meets the application in the regenerated polyolefin plastic resin.

[0012] Optionally, the preparation method of the initial product slurry is as follows: rutile titanium dioxide initial product is added to water for slurry beating and dispersion, the pH is adjusted to 9.3-9.8, a slurry with a titanium dioxide concentration of 35-38wt% is prepared; then sodium silicate aqueous solution is added and dispersed, and the slurry is ground and sieved to control the particle size of the slurry to be 0.15-0.25μm, the titanium dioxide concentration of the system is adjusted to 20-24wt% by adding water, and the pH is adjusted to 9.8-10.8, thereby obtaining the initial product slurry.

[0013] The concentration of the sodium silicate aqueous solution is 160-180g / L in terms of SiO2, and the amount of addition is 0.3-0.4% of the amount of TiO2 in terms of SiO2.

[0014] By adopting the above technical scheme: control the slurry beating, dispersion, grinding and particle size range. Among them, the slurry beating is controlled to obtain a higher titanium dioxide concentration of 35-38wt% slurry, which is beneficial to improve the grinding effect; the pH of the slurry is adjusted to 9.3-10.8 by adding sodium hydroxide solution, which can keep the slurry in a good dispersed state.

[0015] Optionally, the coating method of the silicon dioxide film layer is as follows:

[0016] Under the conditions of temperature 70-85℃ and stirring speed 55-65rpm, the primary slurry is added with sodium silicate aqueous solution, dispersed, first adjusted to pH 9.3-9.6, then reacted for 30-40min, and then adjusted to pH 6.9-7.5 and aged for 70-100min, to obtain the silicon oxide film layer;

[0017] The sodium silicate aqueous solution has a concentration of 95-120g / L of SiO2, and the added amount is 1-1.5% of TiO2 by weight of SiO2.

[0018] By adopting the above technical solution: under the above conditions, a dense amorphous silicon oxide film layer is formed on the surface of titanium dioxide, the crystal lattice defects are blocked, and the light active points on the surface are shielded, so that the oxidation resistance and ultraviolet resistance are improved.

[0019] Optionally, the coating method of the zirconium oxide film layer is as follows:

[0020] The slurry after coating the silicon oxide film layer is cooled to 60-70℃, and under the stirring speed of 65-80rpm, zirconium oxychloride aqueous solution is added dropwise within 110-130min, and sodium hydroxide aqueous solution is added in parallel flow to adjust the slurry pH to 8.2-9.5, reacted for 30-40min, then adjusted to pH 8.0-8.3, and aged for 50-70min, to obtain the zirconium oxide film layer.

[0021] The zirconium oxychloride aqueous solution has a concentration of 110-130g / L of ZrO2, and the added amount is 0.25-0.35% of TiO2 by weight of ZrO2.

[0022] By adopting the above technical solution: under the above conditions, a small amount of dense zirconium oxide film is coated.

[0023] Optionally, the coating method of the aluminum phosphate film layer is as follows:

[0024] The slurry after coating the zirconium oxide film layer is kept at temperature, and under the stirring speed of 50-60rpm, sodium hexametaphosphate aqueous solution is added at one time, dispersed for 30-40min, sodium aluminate aqueous solution is added within 45-65min, and aluminum sulfate solution is added in parallel flow to adjust the slurry pH to 9.4-9.8, aged for 20-30min, then aluminum sulfate solution is added to adjust the slurry pH to 6.0-6.3, and aged for 20-30min, to obtain the aluminum phosphate film layer.

[0025] The sodium hexametaphosphate aqueous solution has a concentration of 140-180g / L of P2O5, and the added amount is 1.0-1.5% of TiO2 by weight of P2O5.

[0026] The sodium aluminate aqueous solution has a concentration of 110-130g / L of Al2O3.

[0027] The concentration of the aluminum sulfate solution is 85-100 g / L in terms of Al2O3.

[0028] Optionally, the coating method of the boehmite aluminum film layer is as follows:

[0029] After the coating of the aluminum phosphate film layer, the temperature of the slurry is adjusted to 50-60℃, and the stirring speed is 55-65 rpm. The sodium metaaluminate aqueous solution is added in 30-50 min, and the aluminum sulfate solution is added in parallel flow to adjust the pH of the slurry to 7.0-8.5. After aging for 40-60 min, the pH is adjusted to 6.8-7.2, and the boehmite aluminum film layer is obtained after aging for 2-2.5 h.

[0030] The concentration of the sodium metaaluminate aqueous solution is 85-120 g / L in terms of Al2O3, and the amount of addition is 0.5-0.7% of TiO2 in terms of weight.

[0031] Optionally, after the boehmite aluminum film layer is obtained, the slurry is filtered, washed, dehydrated and dried, and the resistivity is controlled to be 80-120 Ω·m, and the water content is ≤0.3%.

[0032] Optionally, the specific method of the organic coating treatment is as follows: an organic coating agent is added at the outlet of the jet mill for organic coating treatment, and the amount of addition is 0.25-0.45% of TiO2 in terms of weight.

[0033] Optionally, the organic coating agent is one of dimethyl silicone oil, trimethylol ethane, polysilanol and octyl triethoxysilane.

[0034] In the second aspect, the application provides a titanium dioxide pigment for regenerating polyolefin, which is prepared by the above-mentioned method.

[0035] By using the above technical solution: compared with the existing products, not only the special performance needs are met, but also the amount of addition can be reduced by 5-8% under the same conditions, and the service life of the polyolefin product is increased by 2-3 times.

[0036] In summary, the application has the following beneficial effects:

[0037] 1. The application uses a lower titanium dioxide slurry concentration as raw material, different coating temperatures, limited coating layer types, and different coating times and pH values to make the obtained product have antioxidant degradation, yellowing and better weather resistance in the application of regenerating polyolefin plastic system. Then organic coating treatment is carried out to enhance the compatibility, dispersibility and processing fluidity of the product in the polyolefin plastic system, and finally a titanium dioxide pigment product that meets the application in the regenerating polyolefin plastic resin is obtained.

[0038] 2、The application is coated under different film temperature, lower concentration of coating agent, different stirring intensity, and different coating time and PH value, so that the low content but dense silicon oxide and zirconium oxide film layer, and special aluminum phosphate and boehmite type aluminum oxide film layer are formed. DETAILED DESCRIPTION

[0039] The application is further described in detail below in combination with examples.

[0040] The physical parameters of the rutile titanium dioxide primary product produced by the sulfuric acid process are as follows: L value 94%, b value 3.5, titanium dioxide content 98%, rutile content 97.5%, particle size range 0.10-0.46 μm, and Fe impurity content 50 ppm. Example 1

[0041] A preparation method of a titanium dioxide pigment for recycled polyolefin, comprising the following steps:

[0042] S1, preparation of the primary product slurry: 10 kg of rutile titanium dioxide primary product produced by the sulfuric acid process is added with deionized water for slurry preparation and dispersion, and an aqueous sodium hydroxide solution is added to adjust the system pH to 9.3 to obtain a slurry with a titanium dioxide concentration of 35 wt%; then an aqueous sodium silicate solution (concentration of SiO2 is 160 g / L, and the amount of sodium silicate added is 0.3% of the amount of TiO2 in terms of SiO2) is added for dispersion for 30 min, and the slurry is subjected to sand milling, screening and cyclone classification grinding and dispersion treatment; 50 wt% of the slurry with a titanium dioxide particle size of 0.15-0.25 μm is taken, water is added to adjust the titanium dioxide concentration of the system to 20 wt%, and an aqueous sodium hydroxide solution is added to adjust the system pH to 9.8 to obtain the primary product slurry; the concentration of the aqueous sodium hydroxide solution is 20 wt%;

[0043] Silicon oxide film layer coating: the primary product slurry is heated to 70℃, and an aqueous sodium silicate solution (concentration of SiO2 is 95 g / L, and the amount of sodium silicate added is 1% of the weight of TiO2 in terms of SiO2) is added to the primary product slurry for dispersion under a stirring speed of 55 rpm, hydrochloric acid is added dropwise to adjust the system pH to 9.3 within 130 min, and then the slurry is reacted for 30 min, and then hydrochloric acid is added to adjust the pH to 6.9 for aging for 70 min to obtain the silicon oxide film layer; the concentration of the hydrochloric acid is 7 wt%;

[0044] Zirconia coating: The slurry coated with the silica film was cooled to 60℃. While stirring at 65 rpm, a zirconium oxychloride aqueous solution (concentration of 110 g / L based on ZrO2, and the amount of zirconium oxychloride added being 0.25% of the weight of TiO2 based on ZrO2) was added dropwise over 110 min. Simultaneously, a sodium hydroxide aqueous solution was added to adjust the pH of the system to 8.2. After reacting for 30 min, hydrochloric acid was added to adjust the pH to 8.0, and the mixture was allowed to mature for 50 min to obtain the zirconium oxide film. The concentration of the sodium hydroxide aqueous solution was 10 wt%; the concentration of the hydrochloric acid was 7 wt%.

[0045] Aluminum phosphate film coating: Maintaining the temperature of the slurry after coating with zirconia film, add sodium hexametaphosphate aqueous solution (concentration of 140 g / L based on P2O5, and the amount added is 1.0% of the weight of TiO2 based on P2O5) in one go at a stirring speed of 50 rpm and disperse for 30 min. Then, add sodium aluminate aqueous solution dropwise at 45 min, and simultaneously add aluminum sulfate solution in parallel to adjust the pH of the system to 9.4. After maturation for 20 min, add aluminum sulfate solution again to adjust the pH of the system to 6.0 and mature for another 20 min to obtain the aluminum phosphate film. The concentration of sodium aluminate aqueous solution is 110 g / L based on Al2O3, and the concentration of aluminum sulfate solution is 85 g / L based on Al2O3.

[0046] Boehm-type aluminum film coating: The temperature of the slurry coated with aluminum phosphate film was adjusted to 50℃. At a stirring speed of 55 rpm, sodium aluminate aqueous solution (concentration of 85 g / L based on Al2O3, with Al2O3 accounting for 0.5% of TiO2 weight) was added over 30 min. Simultaneously, aluminum sulfate solution was added in parallel to adjust the pH of the system to 7.0. After maturation for 40 min, 10 wt% hydrochloric acid was added to adjust the pH of the system to 6.8, and maturation for 2 h was completed to obtain the Boehm-type aluminum film. The aluminum sulfate solution concentration was 85 g / L based on Al2O3.

[0047] S2. The slurry coated with the Boehm-type aluminum film layer is filtered, washed, dehydrated and dried in sequence to control its resistivity to 80-120Ω·m and water content to ≤0.3%. Then it is subjected to air jet pulverization and grinding. An organic coating agent (octyltriethoxysilane, added at 0.3% of the weight of TiO2) is added at the outlet of the air jet mill to perform organic coating treatment, thus obtaining titanium dioxide for recycled polyolefins. Example 2

[0048] A method for preparing titanium dioxide pigment for recycled polyolefins includes the following steps:

[0049] S1, Preparation of the primary slurry: To 10 kg of the primary product of the sulphuric acid process for producing rutile titanium dioxide, deionized water was added for slurry dispersion, and sodium hydroxide solution was added to adjust the pH of the system to 9.5 to prepare a slurry containing 37 wt% of titanium dioxide; then sodium silicate solution (concentration of 170 g / L of SiO2, and the amount of sodium silicate added was 0.35% of the amount of TiO2 in terms of SiO2) was added for dispersion for 30 min, and the slurry was treated by sand milling, screening and cyclone classification grinding and dispersion; 50 wt% of the slurry with a particle size of 0.15-0.25 μm was taken, water was added to adjust the titanium dioxide concentration of the system to 22 wt%, and sodium hydroxide solution was added to adjust the pH of the system to 10.3 to obtain the primary slurry; wherein the concentration of the sodium hydroxide solution was 20 wt%;

[0050] Coating of the silicon oxide film layer: the primary slurry was heated to 70°C, and sodium silicate solution (concentration of 105 g / L of SiO2, and the amount of sodium silicate added was 1.25% of the weight of TiO2 in terms of SiO2) was added to the primary slurry for dispersion under a stirring speed of 55 rpm, hydrochloric acid was added dropwise to adjust the pH of the system to 9.5 within 140 min, and then the reaction was carried out for 35 min, and then hydrochloric acid was added to adjust the pH to 7.2 for aging for 85 min to obtain the silicon oxide film layer; wherein the concentration of the hydrochloric acid was 7 wt%;

[0051] Coating of the zirconium oxide film layer: the slurry after coating of the silicon oxide film layer was cooled to 65°C, and zirconium oxychloride solution (concentration of 110 g / L of ZrO2, and the amount of zirconium oxychloride added was 0.25% of the weight of TiO2 in terms of ZrO2) was added dropwise within 120 min while sodium hydroxide solution was added to adjust the pH of the system to 9.0 in a parallel flow, and then the reaction was carried out for 35 min, and then hydrochloric acid was added to adjust the pH to 8.2 for aging for 60 min to obtain the zirconium oxide film layer; wherein the concentration of the sodium hydroxide solution was 10 wt%; and the concentration of the hydrochloric acid was 7 wt%;

[0052] Coating of the aluminum phosphate film layer: the temperature of the slurry after coating of the zirconium oxide film layer was maintained, and sodium hexametaphosphate solution (concentration of 160 g / L of P2O5, and the amount added was 1.25% of the weight of TiO2 in terms of P2O5) was added once for dispersion for 35 min under a stirring speed of 55 rpm, sodium metaphosphate solution and aluminum sulfate solution were added dropwise within 55 min while adjusting the pH of the system to 9.6 in a parallel flow for aging for 25 min, and then aluminum sulfate solution was added to adjust the pH to 6.2 for aging for 25 min to obtain the aluminum phosphate film layer; wherein the concentration of the sodium metaphosphate solution was 120 g / L of Al2O3; and the concentration of the aluminum sulfate solution was 100 g / L of Al2O3;

[0053] Coating boehmite aluminum film layer: the temperature of the slurry after coating the aluminum phosphate film layer is adjusted to 55℃, and under the stirring speed of 60 rpm, sodium metaaluminate aqueous solution (concentration of 100 g / L of Al2O3, and the amount of addition of 0.6% of Al2O3 based on the weight of TiO2) is added dropwise within 40 min while the aluminum sulfate solution is added in parallel flow to adjust the pH of the system to 8.0, and then aged for 50 min, and then 10 wt% hydrochloric acid is added to adjust the pH of the system to 7.0, and then aged for 2.2 h, to obtain the boehmite aluminum film layer; wherein the concentration of the aluminum sulfate solution is 100 g / L of Al2O3;

[0054] S2, the slurry after coating the boehmite aluminum film layer is sequentially subjected to filtration washing, dewatering and drying, the resistivity is controlled to be 80-120 Ω·m, the water content is ≤0.3%, then airflow crushing, grinding, and adding an organic coating agent (dimethyl silicone oil, the amount of addition is 0.35% of TiO2 by weight) at the outlet position of the steam powder machine for organic treatment, to obtain the titanium dioxide pigment for regenerating polyolefin. Example 3

[0055] A preparation method of a titanium dioxide pigment for regenerating polyolefin, comprising the following steps:

[0056] S1, preparation of the initial product slurry: add deionized water to 10 kg of rutile titanium dioxide initial product produced by sulfuric acid process to make slurry, and add 20 wt% sodium hydroxide aqueous solution to adjust the pH of the system to 9.8 to obtain a slurry containing 38 wt% titanium dioxide; then add sodium silicate aqueous solution (concentration of 180 g / L of SiO2, and the amount of addition of sodium silicate is 0.4% of SiO2 based on the amount of TiO2) for dispersion for 30 min, and then subjected to sand grinding, screening and cyclone classification grinding and dispersion treatment; take 50 wt% slurry with a particle size of 0.15-0.25 μm, add water to adjust the concentration of titanium dioxide in the system to 24 wt%, and add sodium hydroxide aqueous solution to adjust the pH of the system to 10.8, to obtain the initial product slurry;

[0057] Coating silicon oxide film layer: the initial product slurry is heated to 85℃, and under the stirring speed of 65 rpm, sodium silicate aqueous solution (concentration of 120 g / L of SiO2, and the amount of addition of sodium silicate is 1.5% of SiO2 based on the weight of TiO2) is added to the initial product slurry for dispersion, and hydrochloric acid is added dropwise within 150 min to adjust the pH of the system to 9.6, and then reacted for 40 min, and then additional hydrochloric acid is added to adjust the pH to 7.5, and then aged for 100 min, to obtain the silicon oxide film layer; wherein the concentration of the hydrochloric acid is 8 wt%;

[0058] Coating zirconium oxide film layer: the slurry after coating the silicon oxide film layer is cooled to 70℃, and under the stirring speed of 80 rpm, zirconium oxychloride aqueous solution (the concentration is 130 g / L in terms of ZrO2, and the added amount of zirconium oxychloride is 0.30% of TiO2 in terms of ZrO2) is added dropwise within 130 min, and sodium hydroxide aqueous solution is added simultaneously to adjust the pH of the system to 9.5, and then the reaction is carried out for 40 min, and then sodium hydroxide aqueous solution is added to adjust the pH to 8.3, and then the aging is carried out for 70 min, to obtain the zirconium oxide film layer; wherein the concentration of the sodium hydroxide aqueous solution is 10 wt%.

[0059] Coating aluminum phosphate film layer: the temperature of the slurry after coating the zirconium oxide film layer is maintained, and under the stirring speed of 60 rpm, sodium hexametaphosphate aqueous solution (the concentration is 160 g / L in terms of P2O5, and the added amount is 1.0% of TiO2 in terms of P2O5) is added at one time, and the dispersion is carried out for 40 min, and sodium metaphosphate aqueous solution and aluminum sulfate solution are added dropwise simultaneously within 65 min to adjust the pH of the system to 9.8, and then the aging is carried out for 30 min, and then aluminum sulfate solution is added to adjust the pH of the system to 6.3, and then the aging is carried out for 30 min, to obtain the aluminum phosphate film layer; wherein the concentration of the sodium metaphosphate aqueous solution is 130 g / L in terms of Al2O3; and the concentration of the aluminum sulfate solution is 95 g / L in terms of Al2O3.

[0060] Coating boehmite film layer: the temperature of the slurry after coating the aluminum phosphate film layer is adjusted to 60℃, and under the stirring speed of 65 rpm, sodium metaphosphate aqueous solution (the concentration is 120 g / L in terms of Al2O3, and the added amount is 0.7% of TiO2 in terms of Al2O3) is added within 50 min, and aluminum sulfate solution is added simultaneously to adjust the pH of the system to 8.5, and then the aging is carried out for 60 min, and then hydrochloric acid with the concentration of 10 wt% is added to adjust the pH of the system to 7.2, and then the aging is carried out for 2.5 h, to obtain the boehmite film layer; wherein the concentration of the aluminum sulfate solution is 95 g / L in terms of Al2O3.

[0061] S2, the slurry after coating the boehmite film layer is sequentially subjected to filtration, washing, dehydration and drying, the resistivity is controlled to be 80-120 Ω·m, the water content is ≤0.3%, and then airflow crushing, grinding, and organic treatment are carried out by adding an organic coating agent (polysilicone, the added amount is 0.45% of TiO2 in terms of weight) at the outlet position of the steam pulverizer, to obtain the regenerated titanium dioxide pigment for polyolefin.

[0062] Comparative Example 1: a general rutile titanium dioxide pigment, the manufacturer is Longbai Group Co., Ltd., and the model number is 996.

[0063] Comparative Example 2: a rutile titanium dioxide pigment for plastic, the manufacturer is Panzhihua Oriental Titanium Industry Co., Ltd., and the model number is R5568.

[0064] Comparative Example 3: a sharp titanium type titanium dioxide pigment, the manufacturer is Guangxi Jinmao Titanium Industry Co., Ltd., and the model number is JMA110.

[0065] Comparative Example 4: A titanium dioxide pigment, which differs from Example 1 in that the preparation of the crude slurry in step S1 and the conditions for coating the boehmite aluminum film layer are different, as follows:

[0066] S1, Preparation of the crude slurry: To 10 kg of crude rutile titanium dioxide produced by the sulfuric acid process, deionized water was added for slurry dispersion, and a sodium hydroxide aqueous solution was added to adjust the system pH to 9.3 to obtain a slurry with a titanium dioxide concentration of 30 wt%. Then a sodium silicate aqueous solution (concentration of 160 g / L of SiO2, and the amount of sodium silicate added was 0.3% of the amount of TiO2) was added for dispersion for 30 min, and the slurry was treated by sand milling, screening, and cyclone classification and grinding dispersion to control the particle size in the range of 0.05-0.1 μm. The system was adjusted to a titanium dioxide concentration of 18 wt% by adding water, and the system pH was adjusted to 9.8 by adding a sodium hydroxide aqueous solution. The crude slurry was obtained, wherein the concentration of the sodium hydroxide aqueous solution was 20 wt%.

[0067] Coating of the silicon oxide film layer: The crude slurry was heated to 65°C, and a sodium silicate aqueous solution (concentration of 95 g / L of SiO2, and the amount of sodium silicate added was 1% of the weight of TiO2) was added to the crude slurry under stirring at a stirring speed of 55 rpm. Hydrochloric acid was added dropwise to adjust the system pH to 9.3 within 130 min, and then the reaction was carried out for 30 min. After the pH was adjusted to 6.9 by adding hydrochloric acid, the slurry was aged for 70 min to obtain the silicon oxide film layer. The concentration of the hydrochloric acid was 7 wt%.

[0068] Coating of the zirconium oxide film layer: The slurry after coating the silicon oxide film layer was cooled to 55°C, and a zirconium oxychloride aqueous solution (concentration of 110 g / L of ZrO2, and the amount of zirconium oxychloride added was 0.25% of the weight of TiO2) was added dropwise within 110 min while a sodium hydroxide aqueous solution was added to adjust the system pH to 8.2. The reaction was carried out for 30 min, and then the pH was adjusted to 8.0 by adding hydrochloric acid. The slurry was aged for 50 min to obtain the zirconium oxide film layer. The concentration of the sodium hydroxide aqueous solution was 10 wt%, and the concentration of the hydrochloric acid was 7 wt%.

[0069] Comparative Example 5: A titanium dioxide pigment, which differs from Example 1 in that the preparation of the crude slurry in step S1 and the conditions for coating the silicon oxide film layer are different, as follows:

[0070] S1, Preparation of the primary slurry: To 10 kg of the primary product of the sulphuric acid process for producing rutile titanium dioxide, deionized water was added for slurry dispersion, and sodium hydroxide aqueous solution was added to adjust the pH of the system to 9.3 to prepare a slurry containing 42 wt% of titanium dioxide; then sodium silicate aqueous solution (the concentration of SiO2 was 160 g / L, and the amount of sodium silicate added was 0.3% of the amount of TiO2 in terms of SiO2) was added for dispersion for 30 min, and the slurry was treated by sand milling, screening and cyclone classification grinding and dispersion to control the particle size of the slurry in the range of 0.3-0.4 μm, and then water was added to adjust the concentration of titanium dioxide in the system to 26 wt%, and sodium hydroxide aqueous solution was added to adjust the pH of the system to 9.8 to obtain the primary slurry; wherein the concentration of the sodium hydroxide aqueous solution was 20 wt%;

[0071] Coating of the silicon oxide film layer: the primary slurry was heated to 90℃, and sodium silicate aqueous solution (the concentration of SiO2 was 95 g / L, and the amount of sodium silicate added was 1% of the weight of TiO2 in terms of SiO2) was added to the primary slurry for dispersion under the stirring speed of 55 rpm, and hydrochloric acid was added dropwise to adjust the pH of the system to 9.3 within 130 min, and then the reaction was carried out for 30 min, and then hydrochloric acid was added to adjust the pH to 6.9 for aging for 70 min to obtain the silicon oxide film layer; wherein the concentration of the hydrochloric acid was 7 wt%;

[0072] Coating of the zirconium oxide film layer: the slurry after coating of the silicon oxide film layer was cooled to 75℃, and zirconyl hydroxide aqueous solution (the concentration of ZrO2 was 110 g / L, and the amount of zirconyl hydroxide added was 0.25% of the weight of TiO2 in terms of ZrO2) was added dropwise within 110 min while sodium hydroxide aqueous solution was added to adjust the pH of the system to 8.2 for reaction for 30 min, and then hydrochloric acid was added to adjust the pH to 8.0 for aging for 50 min to obtain the zirconium oxide film layer; wherein the concentration of the sodium hydroxide aqueous solution was 10 wt%; and the concentration of the hydrochloric acid was 7 wt%.

[0073] The titanium dioxide pigments (also referred to as titanium white) prepared in the examples and comparative examples were subjected to the following performance tests, and the test results are recorded in Table 1.

[0074] Basic indexes: 4 g of the titanium dioxide pigment was blended with 196 g of PP resin to obtain a mixture, and the mixture was added to a HTW-500x2 horizontal injection molding machine to obtain a sample plate with a thickness of 2 mm, and the sample plate was subjected to detection by a CM-23d spectrophotometer to obtain the L value, b value, whiteness and yellowing index.

[0075] 2, Filter pressure value (FPV): the sample and linear low density polyethylene (LLDPE) were mixed by a double screw extruder to prepare a 70% concentration color masterbatch, and the color masterbatch was diluted with a base resin to obtain a mixture containing 14% of titanium white, and then the filter pressure value (FPV) was detected by a single screw extruder to represent the dispersibility of the titanium white, and a smaller value indicated a better dispersibility in the system.

[0076] 3. Light resistance UV stability: 4 g of titanium dioxide pigment is blended with 196 g of PP resin to obtain a mixture, which is added to a HTW-500x2 horizontal injection molding machine to obtain a sample plate with a thickness of 2 mm, the sample plate is detected by a CM-23d spectrophotometer to obtain L value, a value, b value and whiteness; then it is placed in a UV aging box and irradiated for 4 hours in a 700W UV340 aging box, and the L value, a value, b value and whiteness are determined again; the difference between the two detections is ΔL, Δa, Δb, and ΔE is calculated according to ΔE = (ΔL 2 + Δa 2 + Δb 2 ) 1 / 2 The light resistance aging color difference ΔE value is calculated.

[0077] 4. 250℃ temperature resistance: the sample is obtained by pressing the titanium dioxide powder with a hand pressure cake machine, the sample is first detected by a CM-23d spectrophotometer to obtain L value, a value, b value and whiteness index, then it is heated at 250℃ in a constant temperature electric heating air drying oven for 20 minutes, and the L value, a value, b value and whiteness index are measured again after the sample is cooled, the difference between the two detections is ΔL, Δa, Δb, and ΔE is calculated according to ΔE = (ΔL 2 + Δa 2 + Δb 2 ) 1 / 2 The 250℃ temperature resistance color difference ΔE value is calculated.

[0078] Table 1: Performance test results

[0079]

[0080] As shown in Table 1, the titanium dioxide products prepared in Examples 1-3 have a whiteness of up to 94.36 and a yellowing of as low as 1.06 after being blended with PP resin, while the whiteness of commercially available products is 91-93 and the yellowing can be as high as 3.15, indicating that the whiteness is low and the yellowing is large, which shows that the titanium dioxide pigment prepared in the application has higher whiteness and smaller yellowing when applied in a resin system. At the same time, the filter pressure value is smaller, the color difference value after light aging and temperature resistance detection is smaller, which shows that the dispersion and weather resistance of the patent product in the plastic system are better, and it better meets the needs of the properties of titanium dioxide pigment for recycled polyolefin.

[0081] Examples 1, Comparative Examples 4-5 are compared, and the difference between Comparative Examples 4-5 and Example 1 is that the initial slurry with different concentrations and different particle size ranges is used as raw material, and the temperature for coating the silicon oxide film and the zirconium oxide film is different, and the performance of the prepared titanium dioxide pigment is decreased.

[0082] The embodiments are only illustrative of the present application, and are not intended to limit the present application, and those skilled in the art can make modifications to the embodiments without creative contribution after reading the specification, but as long as the modifications are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A method for producing titanium dioxide pigments for recycling polyolefins, characterized by, The method comprises the following steps: S1, taking the rutile titanium dioxide slurry with a concentration of 20-24wt% and a particle size of 0.15-0.25μm as raw material, coating a silicon oxide film layer at 70-85℃, coating a zirconium oxide film layer at 60-70℃, and then coating an aluminum phosphate film layer and a boehmite aluminum oxide film layer at 50-65℃, respectively; S2, after filtration, washing, dehydration and drying, and airflow crushing, organic coating treatment is performed, and the product is obtained.

2. The method for producing titanium dioxide pigment for recycled polyolefin according to claim 1, characterized by, The preparation method of the slurry comprises the following steps: adding the rutile titanium dioxide into water to be dispersed and pulped, adjusting the pH to 9.3-9.8, and preparing a slurry with a titanium dioxide concentration of 35-38wt%; then adding a sodium silicate aqueous solution, dispersing, grinding, and sieving, controlling the particle size of the slurry to be 0.15-0.25μm, adjusting the titanium dioxide concentration of the system to be 20-24wt%, and adjusting the pH to be 9.8-10.8, and the slurry is obtained. The sodium silicate aqueous solution has a concentration of 160-180g / L of SiO2, and the amount of the sodium silicate aqueous solution accounts for 0.3-0.4% of the amount of TiO2.

3. The method for producing titanium dioxide pigment for recycled polyolefin according to claim 1, characterized by, The coating method of the silicon oxide film layer is as follows: The silicon oxide film layer is obtained by adding a sodium silicate aqueous solution into the slurry at a temperature of 70-85℃ and a stirring speed of 55-65rpm, adjusting the pH to 9.3-9.6 first, and then reacting for 30-40min, and adjusting the pH to 6.9-7.5 and aging for 70-100min. The sodium silicate aqueous solution has a concentration of 95-120g / L of SiO2, and the amount of the sodium silicate aqueous solution accounts for 1-1.5% of the weight of TiO2.

4. The method for producing titanium dioxide pigment for recycled polyolefin according to claim 1, characterized by, The coating method of the zirconium oxide film layer is as follows: The zirconium oxide film layer is obtained by cooling the slurry after coating the silicon oxide film layer to 60-70℃, adding a zirconium oxychloride aqueous solution dropwise at a stirring speed of 65-80rpm within 110-130min, and adding a sodium hydroxide aqueous solution to adjust the pH of the slurry to 8.2-9.5 at the same time, reacting for 30-40min, adjusting the pH to 8.0-8.3, and aging for 50-70min. The zirconium oxychloride aqueous solution has a concentration of 110-130g / L of ZrO2, and the amount of the zirconium oxychloride aqueous solution accounts for 0.25-0.35% of the weight of TiO2.

5. The method for producing titanium dioxide pigment for recycled polyolefin according to claim 1, characterized by, The coating method of the aluminum phosphate film layer is as follows: The aluminum phosphate film layer is obtained by keeping the temperature of the slurry after coating the zirconium oxide film layer, adding a sodium hexametaphosphate aqueous solution at a stirring speed of 50-60rpm, dispersing for 30-40min, adding a sodium metaaluminate aqueous solution within 45-65min, adding an aluminum sulfate solution to adjust the pH of the slurry to 9.4-9.8 at the same time, aging for 20-30min, adding an aluminum sulfate solution to adjust the pH of the slurry to 6.0-6.3, and aging for 20-30min. The sodium hexametaphosphate aqueous solution has a concentration of 140-180g / L of P2O5, and the amount of the sodium hexametaphosphate aqueous solution accounts for 1.0-1.5% of the weight of TiO2. The sodium metaaluminate aqueous solution has a concentration of 110-130g / L of Al2O3. The concentration of the aluminum sulfate solution is 85-100 g / L in terms of Al2O3.

6. The method for producing titanium dioxide pigment for recycled polyolefin according to claim 1, characterized by, The coating method of the boehmite aluminum film layer is as follows: After the slurry is coated with the aluminum phosphate film layer, the temperature of the slurry is adjusted to 50-60 DEG C, and the stirring speed is adjusted to 55-65 rpm; then, the sodium metaaluminate aqueous solution is added into the slurry in 30-50 min, and the aluminum sulfate solution is added into the slurry in parallel flow to adjust the pH of the slurry to 7.0-8.5; after aging for 40-60 min, the pH is adjusted to 6.8-7.2, and the slurry is aged for 2-2.5 h to obtain the boehmite aluminum film layer. The concentration of the sodium metaaluminate aqueous solution is 85-120 g / L in terms of Al2O3, and the amount of the sodium metaaluminate aqueous solution added is 0.5-0.7% of TiO2 in terms of weight.

7. The method of claim 1, wherein the method is characterized by: After the slurry is coated with the boehmite aluminum film layer, the slurry is filtered, washed, dehydrated and dried, and the resistivity of the slurry is controlled to be 80-120 ohm-m, and the water content of the slurry is controlled to be less than or equal to 0.3%.

8. The method for producing titanium dioxide pigment for recycled polyolefin according to claim 1, characterized by, The specific method of the organic coating treatment is as follows: an organic coating agent is added into the outlet of the jet mill for the organic coating treatment, and the amount of the organic coating agent added is 0.25-0.45% of TiO2 in terms of weight.

9. The method of producing titanium dioxide pigments for recycled polyolefins according to claim 8, characterized in that: The organic coating agent is one of dimethyl silicone oil, trimethylol ethane, polysilanol and octyl triethoxysilane.

10. A titanium white pigment characterized in that: The titanium dioxide pigment for the regenerated polyolefin is prepared by the method of any one of claims 1-9. The concentration of the aluminum sulfate solution is 85-100 g / L in terms of Al2O3. The coating method of the boehmite aluminum film layer is as follows: After the slurry is coated with the aluminum phosphate film layer, the temperature of the slurry is adjusted to 50-60 DEG C, and the stirring speed is adjusted to 55-65 rpm; then, the sodium metaaluminate aqueous solution is added into the slurry in 30-50 min, and the aluminum sulfate solution is added into the slurry in parallel flow to adjust the pH of the slurry to 7.0-8.5; after aging for 40-60 min, the pH is adjusted to 6.8-7.2, and the slurry is aged for 2-2.5 h to obtain the boehmite aluminum film layer. The concentration of the sodium metaaluminate aqueous solution is 85-120 g / L in terms of Al2O3, and the amount of the sodium metaaluminate aqueous solution added is 0.5-0.7% of TiO2 in terms of weight. After the slurry is coated with the boehmite aluminum film layer, the slurry is filtered, washed, dehydrated and dried, and the resistivity of the slurry is controlled to be 80-120 ohm-m, and the water content of the slurry is controlled to be less than or equal to 0.3%. The specific method of the organic coating treatment is as follows: an organic coating agent is added into the outlet of the jet mill for the organic coating treatment,

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