A method for preparing a white pigment with high solar reflectance

Abstract

The application discloses a preparation method of a high-solar-reflection white pigment, adopts a heterogeneous nucleation principle, takes ethyl titanate as a titanium source, coats titanium dioxide on barium sulfate as an inner core to generate barium sulfate-titanium white composite particles, inactivates the newborn titanium white by wrapping with sodium silicate, and carries out aging, separation, drying and dispersion to obtain the high-solar-reflection white pigment. The white pigment with titanium white wrapped on barium sulfate is pure white in color, has high Hunter whiteness, and has a high solar reflection ratio TSR>98% in a 200nm-2500nm wave band. Compared with the large-particle-size infrared reflection titanium white powder, the white pigment is more pure white in color and has a higher reflection ratio in a visible light region. The white pigment produced by the application has low color fading, the addition amount of infrared reflection color paste is saved by 20-40% when the white pigment is used to adjust color of white paint, the white pigment is more economical to use, and the gross profit space is higher. The application is the barium sulfate-titanium white powder composite pigment, and has obvious cost advantage.

Description

Technical Field

[0001] This invention relates to the field of white pigment preparation, and particularly to a method for preparing a white pigment with high solar reflectance. Background Technology

[0002] As global temperatures rise, the world is encouraging the research and development and production of low-carbon, environmentally friendly, and energy-saving products. Near-infrared reflective pigments are being used in reflective insulation products to create high solar reflectance products. In the coatings industry, high solar reflectance coatings such as stone-like paint, multi-color paint, and elastic flat paint are becoming increasingly popular. Due to their end-use applications, coatings with high solar reflectance are gaining popularity on the surfaces of coiled aluminum and steel. Chemical storage tanks and grain silos using high solar reflectance coatings maintain low indoor temperatures, ensuring the safety of stored chemicals and grains. The promotion of white roofs also aligns with the demand for cool roofs in the modern era, reducing air conditioning use, saving energy, and reducing carbon emissions, while ensuring that stored grains do not ferment at high temperatures.

[0003] Currently, the market offers a complete range of high solar reflectance pigments in various colors, including yellow, orange, red, blue, green, black, and white. These colored pigments primarily rely on high near-infrared reflectance to achieve high total solar reflectance. These colored pigments include coated, high-temperature calcined, and co-precipitated types. Coated pigments are prepared by depositing pigments that selectively absorb visible light and transmit infrared light onto a high-infrared reflectance substrate. For example, green Cr2O3 is deposited on the surface of high-solar-reflectance flake aluminum powder to prepare a core-shell structured, low-brightness, low-gloss infrared reflective pigment. High-temperature calcined pigments utilize a mixture of metal oxides, nitrates, acetates, or even oxides in a high-temperature calcination solid-phase reaction. At high temperatures, metal ions and oxygen ions rearrange to form stable composite metal oxides with structures similar to spinel or rutile. Examples of these pigments include titanium chromium yellow, cobalt blue, and iron chromium black. Currently, high solar reflectance white pigments are infrared reflective titanium dioxide. Huntsman's ALTIRIS® infrared reflective pigment W400 modifies solar reflectivity through crystal size. The product's initial crystal size is 400nm, featuring a large-particle titanium dioxide (TiO2) core, combined with a silica and alumina shell. Organic modification yields a large-size, narrow-particle-distribution titanium dioxide pigment. Compared to ordinary titanium dioxide, this titanium dioxide reflects a larger proportion of near-infrared light while maintaining high hiding power and tinting strength. Ishihara's PFR-404 from Japan exhibits excellent near-infrared reflectivity, while Jiangsu Panhua Chemical's titanium dioxide IR-1000 from my country is an infrared-reflective titanium dioxide prepared using the sulfuric acid method.

[0004] Currently, the high solar reflectance white pigments on the market are mainly of these types: large-particle-size titanium dioxide with excellent near-infrared reflectance. Huntsman Infrared Reflective Titanium Dioxide from the United States offers three products with high, medium, and low tinting strength respectively. Ishihara PFR-404 from Japan is another product with excellent near-infrared reflectance and medium tinting strength.

[0005] Total Solar Reflectance (TSR) = Ultraviolet Reflectance + Visible Reflectance + Infrared Reflectance. A high TSR material is achieved by exhibiting good reflection in the ultraviolet, visible, and near-infrared regions. Ordinary titanium dioxide has good reflection in the ultraviolet and visible light regions, but low reflection in the near-infrared region. Increasing the original particle size of titanium dioxide blocks more infrared light transmission, thus improving the TSR. Huntsman's infrared-reflecting titanium dioxide pigment has a larger particle size than conventional titanium dioxide pigments, resulting in a very high near-infrared reflectance. However, as the particle size increases, whiteness decreases, appearing yellowish-red and darkening. This decrease in whiteness leads to absorption in the visible light region, affecting reflection in that area. Increasing the particle size sacrifices whiteness and also increases cost. Relying on increasing the particle size to improve the total solar reflectance is not perfect; this method results in a darker, yellowish pigment and higher costs. Summary of the Invention

[0006] The technical problem to be solved by this invention is to overcome the defects of the prior art and provide a method for preparing a white pigment with high solar reflectance. The produced titanium dioxide-coated barium sulfate pigment has high whiteness and high total solar reflectance (TSR≥98%); low tinting strength; and is economical in tinting systems, reducing the amount of pigment used and increasing the product's gross profit margin. Moreover, the white pigment of this invention is a barium sulfate-titanium dioxide composite pigment, which has a cost advantage over infrared reflective titanium dioxide pigments on the market. It solves the problems of large-particle-size infrared reflective titanium dioxide pigments having a dark yellow color and high tinting strength, resulting in high paint costs, and alleviates the pressure of high costs in the preparation of solar reflective products.

[0007] This invention provides the following technical solution:

[0008] This invention utilizes barium sulfate as the core in heterogeneous nucleation and ethyl titanate as the titanium source to precipitate and coat barium sulfate with titanium dioxide to prepare a white pigment. The barium sulfate core is an excellent material for reflecting ultraviolet, visible, and near-infrared light, exhibiting high refractive index and weak tinting strength. Titanium dioxide is also an excellent material for reflecting ultraviolet, visible, and infrared light, possessing high refractive index and strong tinting strength. The titanium dioxide-coated barium sulfate white pigment exhibits high reflectivity in the ultraviolet, visible, and near-infrared regions. Despite the increased particle size, the coated structure maintains a pure white color without yellowing or darkening, and demonstrates strong reflectivity in ultraviolet, visible, and near-infrared light. Simultaneously, barium sulfate's low tinting strength offers significant advantages in color matching systems, allowing for reduced use of infrared reflective pigments to achieve the same color intensity. Therefore, using this invention's white pigment is more economical and offers higher profit margins for products with the same color and solar reflectance ratio (TSR).

[0009] This invention provides a method for preparing a white pigment with high solar reflectance, the steps of which are as follows:

[0010] Step 1: Prepare barium sulfate slurry according to the following weight parts: water 6.00-12.00 parts, defoamer 0.10 parts, dispersant 1.00-1.80 parts, barium sulfate A with particle size D50=300nm 5.00-8.75 parts, barium sulfate B with particle size D50=700nm 12.00-21.00 parts, barium sulfate C with particle size D50=1200nm 3.00-5.25 parts, and water to make up to 100.00 parts;

[0011] Weigh 6-12 parts of water, dispersant, and defoamer into a container and mix them evenly. Add barium sulfate and stir evenly. Disperse at high speed (linear velocity at 10-23 m / s) for 30-40 minutes. Add water to 100 parts to obtain the 20-35% barium sulfate slurry.

[0012] Step 2: Measure 100 parts of ethyl titanate and mix with (3-10) parts of organic alcohol polyether phosphate;

[0013] Step 3: Take 1000g of barium sulfate slurry into a chemical mixing tank, and slowly add 140-500g of a mixture of ethyl titanate and organic alcohol polyether phosphate while stirring continuously. Ethyl titanate hydrolyzes and adsorbs onto the surface of barium sulfate, precipitating and encapsulating the barium sulfate to form barium sulfate-titanium dioxide composite particles. The ethyl titanate-organic alcohol polyether phosphate is added completely over 30-60 minutes, and stirring continues for another 20-30 minutes.

[0014] The fourth step involves adding water-soluble sodium silicate (1%-5%) and titanium dioxide (calculated as SiO2) to the slurry, adjusting the pH to 8-10 with ammonia, heating to 80℃ and reacting at a constant temperature for 3-4 hours; aging overnight, separating and removing the supernatant, spray drying, calcining at 750℃ for 80-100 minutes, and grinding and dispersing to obtain the product.

[0015] As a preferred embodiment of the present invention, the barium sulfate is precipitated barium sulfate produced by the sulfuric acid process or natural barium sulfate, with a Hunter White ≥98, iron impurities <20ppm, and particle size of D10=200nm and D90=1200nm.

[0016] As a preferred embodiment of the present invention, the barium sulfate is composed of three barium sulfates with different particle sizes, wherein barium sulfate A has a D50 of 300 nm, barium sulfate B has a D50 of 700 nm, and barium sulfate C has a D50 of 1200 nm, and the weight ratio among them is A∶B∶C=(20-25)∶60∶(15-20).

[0017] As a preferred embodiment of the present invention, the dispersant used for dispersing barium sulfate is sodium hexametaphosphate.

[0018] As a preferred embodiment of the present invention, the concentration of barium sulfate slurry is 20-35%.

[0019] As a preferred embodiment of the present invention, the ethyl titanate is industrial-grade tetraethyl titanate.

[0020] As a preferred embodiment of the present invention, the organic alcohol polyether phosphate is a monoester or diester or a mixture thereof, such as isomeric alcohol polyether phosphate.

[0021] As a preferred embodiment of the present invention, the ratio of ethyl titanate to organic alcohol polyether phosphate is 100:(3-10).

[0022] As a preferred technical solution of the present invention, the surface deactivation coating agent for newly formed titanium dioxide is industrial-grade water-soluble sodium silicate.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] This solution uses titanium dioxide coated with barium sulfate as a white pigment, resulting in a pure white color with high Hunter whiteness and a high solar reflectance (TSR) of >98% in the 200nm-2500nm wavelength range. Compared to titanium dioxide with large-particle infrared reflectance, it is purer in color and has a higher reflectance in the visible light region.

[0025] This solution uses titanium dioxide-encapsulated barium sulfate white pigment with low tinting strength. When used in tinting paints, it can achieve the same color concentration with less pigment addition, resulting in good tinting economy. Specifically, when preparing products of the same color and solar reflectance, the amount of infrared reflective pigment added using the white pigment produced by this invention is reduced by 20-40%, making the product more economical and increasing the gross profit margin.

[0026] The present invention is a barium sulfate-titanium dioxide composite pigment, which has a significant cost advantage. Attached Figure Description

[0027] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0028] Figure 1 This is a process diagram of the preparation of the present invention. Detailed Implementation

[0029] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention. All identical reference numerals in the drawings refer to the same components.

[0030] Example

[0031] Heterogeneous nucleation occurs when nuclei form on the surface of heterogeneous crystals. The surface energy of heterogeneous nucleation is significantly lower than that of homogeneous nucleation, thus heterogeneous surface nucleation is superior to homogeneous nucleation. This invention uses barium sulfate with different particle sizes (D50) and prepares 20%-35wt% barium sulfate slurry with sodium hexametaphosphate. A mixture of ethyl titanate and organic alcohol polyether phosphate [100:(3-10)] is slowly added under stirring. Ethyl titanate hydrolyzes to generate titanium alcohol sol. Low-concentration newly formed titanium alcohol sol is preferentially adsorbed onto the surface of barium sulfate particles for nucleation and precipitation. With the addition of the ethyl titanate and organic alcohol polyether phosphate mixture, newly formed titanium alcohol sol is continuously adsorbed onto the surface of barium sulfate crystals, continuing to nucleate and grow, thus encapsulating barium sulfate and forming barium sulfate-titanium dioxide particles. Finally, water-soluble sodium silicate is added for coating and inactivation. After aging, separation, drying, and dispersion, the high solar reflectance white pigment of this invention is obtained.

[0032] like Figure 1 This invention provides a method for preparing a white pigment with high solar reflectance, specifically:

[0033] Step 1: Prepare barium sulfate slurry according to the following weight parts: water 6.00-12.00 parts, defoamer 0.10 parts, dispersant 1.00-1.80 parts, barium sulfate A with particle size D50=300nm 5.00-8.75 parts, barium sulfate B with particle size D50=700nm 12.00-21.00 parts, barium sulfate C with particle size D50=1200nm 3.00-5.25 parts, and water to make up to 100.00 parts.

[0034] Weigh 6-12 parts of water, dispersant, and defoamer into a container and mix them evenly. Add barium sulfate and stir evenly. Disperse at high speed (linear velocity of 10-23 m / s) for 30-40 minutes, and add water to make up to 100 parts to obtain the 20-35% barium sulfate slurry.

[0035] Step 2: Measure 100 parts of ethyl titanate and mix with (3-10) parts of organic alcohol polyether phosphate.

[0036] Step 3: Take 1000g of barium sulfate slurry into a chemical mixing tank, and slowly add 140-500g of a mixture of ethyl titanate and organic alcohol polyether phosphate while continuously stirring. The ethyl titanate hydrolyzes and adsorbs onto the surface of the barium sulfate, precipitating and encapsulating the barium sulfate to form barium sulfate-titanium dioxide composite particles. The ethyl titanate-organic alcohol polyether phosphate mixture should be added completely over 30-60 minutes, and stirring should continue for another 20-30 minutes.

[0037] The fourth step involves adding water-soluble sodium silicate (1%-5%) and titanium dioxide (calculated as SiO2) to the slurry, adjusting the pH to 8-10 with ammonia, heating to 80℃ and reacting at a constant temperature for 3-4 hours, aging overnight, separating and removing the supernatant, spray drying, calcining at 750℃ for 80-100 minutes, and grinding and dispersing to obtain the product.

[0038] Example 1

[0039] A method for preparing white pigment with high solar reflectance:

[0040] 1. The main raw materials used in this invention are:

[0041] 1.1.20% barium sulfate slurry contains the following raw materials: 7 parts water, 1.0 part sodium hexametaphosphate dispersant, 0.1 part defoamer D1110, 5.00 parts barium sulfate JB-53 (particle size D50 = 300nm), 12.00 parts barium sulfate BSM-M (particle size D50 = 700nm), 3.00 parts barium sulfate AY-L1200 (particle size D50 = 1200nm), and the remaining water is made up to 100.

[0042] 1.2. Titanium dioxide source: a mixture of ethyl titanate and organic alcohol polyether phosphate, wherein 100 parts of ethyl titanate (industrial grade) and 5 parts of JPC-EP (isomeric alcohol polyether phosphate) are mixed, and the total weight of the mixture is 157.90g.

[0043] 1.3. Coating agent: Sodium silicate NaO·nSiO2 (SiO2 content 29.8%): 3.52g of titanium dioxide (SiO2%) at a dosage of 2%;

[0044] 2. In this embodiment of the invention, the method for preparing high solar reflectance white pigment includes the following steps:

[0045] Step 1: Prepare 20% barium sulfate slurry. Weigh 7 parts water, 1.0 part sodium hexametaphosphate dispersant, and 0.1 part defoamer and mix them evenly in a mixing tank at low speed (5-10 minutes), with a linear velocity of about 2 m / s. Slowly add 5.0 parts JB-53 barium sulfate, 12.0 parts BSM-M barium sulfate, and 3.0 parts AY-L1200 barium sulfate powder and mix well. Then disperse at high speed for 30-40 minutes (linear velocity 15-25 m / s). After the fineness is qualified, slowly add water to the slurry under low speed stirring to dilute the slurry. Add water to make up to 100.0 parts to obtain 20% barium sulfate slurry.

[0046] Step 2: Take 100 parts of ethyl titanate and mix them evenly with 5 parts of JFC-EP;

[0047] Step 3: Take 1000g of 20% barium sulfate slurry into a chemical mixing tank, and slowly add 157.90g of ethyl titanate-JFC-EP mixture while stirring at low speed. The addition should be completed within 30-40 minutes, and stirring should continue for 20-30 minutes.

[0048] Step 4: Add 3.52g of water-soluble sodium silicate to the slurry after step 3 above, adjust the pH to 8-10 with ammonia water, react at a constant temperature of about 80℃ for 3-4 hours. Let it age overnight, separate and remove the supernatant, spray dry, calcine at 750℃ for 80-100 minutes, and grind and disperse to obtain the product.

[0049] The high solar reflectance white pigment obtained in Example 1 has a barium sulfate to titanium dioxide ratio of 4:1, which is a low chromatic power solar reflectance pigment and is used in dark coloring systems.

[0050] Example 2

[0051] A method for preparing a white pigment with high solar reflectance, comprising the following raw materials:

[0052] 1.20% barium sulfate slurry contains the following raw materials: 9.40 parts water, 0.1 parts defoamer, 1.5 parts sodium hexametaphosphate dispersant, 6.90 parts JB-53 barium sulfate, 18.00 parts BSM-M barium sulfate, 5.10 parts AY-L1200 barium sulfate, and the remaining water is made up to 100 parts.

[0053] 2. Titanium dioxide source: 100 parts of ethyl titanate, 6 parts of F1310P (isotridecyl alcohol polyoxyethylene ether phosphate), and 451g of the mixed liquid;

[0054] 3. Coating agent: Sodium silicate NaO·nSiO2 (SiO2 content 29.8%): 2% of titanium dioxide (as SiO2%): 10g;

[0055] The preparation method and process are the same as in Example 1. In Example 2, the white pigment with a barium sulfate:titanium dioxide ratio of 3:2 has higher hiding power and tinting strength than that in Example 1, classifying it as a white pigment with medium tinting strength and high solar reflectance, suitable for use in medium color intensity product systems.

[0056] Performance tests of the white pigments prepared in Examples 1 and 2:

[0057] 1. The whiteness and solar reflectance of the powder tablet were tested, and the results are shown in Table 1. The whiteness of the pure white tablet was higher than that of the calibration white plate used in the instrument, and the total solar reflectance was also higher.

[0058] Table 1. Whiteness and Solar Reflectance (TSR) Tests of Pigment Powder Tableting

[0059]

[0060] 2. The white pigments prepared in Examples 1 and 2 are compared with those prepared into white paint and colored paint using commercially available infrared reflective titanium dioxide, respectively. The data are shown in Table 2.

[0061] 36 parts of white pigment were weighed and mixed with dispersant, defoamer and water to prepare a slurry. 40 parts of pure acrylic emulsion and other formulation additives were added to prepare a coating. The coating was applied to black and white checkered cardboard using a 250μm wet film applicator. After drying, the solar reflectance (TSR) of the coating on the white cardboard was measured at 200nm-2500nm and the near-infrared reflectance (NSR) at 780nm-2500nm using a spectrophotometer. Table 2 shows the test data for the solar reflectance and near-infrared reflectance of the coating on the white cardboard.

[0062] Table 2 shows the solar reflectance (TSR) and near-infrared reflectance (NSR) of the white coating prepared for testing.

[0063]

[0064] Table 2 shows that the white pigment produced by the method of the present invention has higher brightness and whiter color. Although the near-infrared reflectance is lower than that of infrared reflectance titanium dioxide on the market, the total solar reflectance is not lower, but slightly higher.

[0065] 3. A group of samples with low tinting strength was tinted, namely, the paint prepared with low tinting strength infrared reflective titanium dioxide from Example 1 and the market, using infrared reflective black pigment to tint a medium gray. The pigment addition amount and brightness test data are shown in Table 3. At the same pigment addition ratio, the color concentration of the paint film was significantly different. The paint with low tinting strength in Example 1 had a darker color and lower brightness. The gray paint prepared with low tinting strength infrared titanium dioxide from the market, after adding an additional 36.8% pigment, had a color and brightness that were basically consistent with the gray paint prepared with white pigment in Example 1 of this invention.

[0066] Table 3 shows the economic efficiency of white paint tinting tests.

[0067]

[0068] As can be seen from Table 3, when the same amount of pigment is added, the gray lightness L of Example 1 is 39.3, while that of the reference infrared reflective titanium dioxide is 41.7. It takes an additional 36.8% pigment to achieve the same color concentration as the example. The white pigment of the present invention is economical in preparing tinted paint by saving pigment and has obvious color matching potential.

[0069] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a white pigment with high solar reflectance, characterized in that, Using the principle of heterogeneous nucleation, titanium dioxide is coated with barium sulfate as a core using ethyl titanate as the titanium source to generate barium sulfate-titanium dioxide composite particles. The newly formed titanium dioxide is then inactivated by encapsulating it with sodium silicate. After aging, separation, drying, and dispersion, the high solar reflectance white pigment is obtained. The formulation and process are as follows: Step 1: Weigh 6-12 parts water, 1.00-1.80 parts dispersant, and 0.10 parts defoamer into a container and mix them evenly. Add 20-35 parts barium sulfate and stir evenly. Disperse at high speed for 30-40 minutes at a linear velocity of 10-23 m / s. Add water to make up to 100 parts to obtain a barium sulfate slurry with a concentration of 20-35 wt%. Step 2: Measure 100 parts of ethyl titanate and mix with 3-10 parts of organic alcohol polyether phosphate; Step 3: Take 1000g of barium sulfate slurry into a chemical mixing tank, and slowly add 140-500g of a mixture of ethyl titanate and organic alcohol polyether phosphate while stirring continuously. Ethyl titanate hydrolyzes and adsorbs onto the surface of barium sulfate, precipitating and encapsulating the barium sulfate to form barium sulfate-titanium dioxide composite particles. The ethyl titanate-organic alcohol polyether phosphate is added completely over 30-60 minutes, and stirring continues for another 20-30 minutes. The fourth step involves adding water-soluble sodium silicate to the slurry, the amount of which is 1%-5% of the titanium dioxide calculated as SiO2. The pH is adjusted to 8-10 with ammonia water, and the temperature is raised to 80℃ and kept constant for 3-4 hours. The mixture is then aged overnight, the upper clear liquid is separated and removed, spray-dried, calcined at 750℃ for 80-100 minutes, and then ground and dispersed to obtain the product. The barium sulfate is precipitated barium sulfate produced by the sulfuric acid process or natural barium sulfate, with a Hunter White ≥98, iron impurities <20ppm, and particle size of D10=200nm and D90=1200nm. The barium sulfate is composed of three different particle sizes: barium sulfate A with a D50 of 300 nm, barium sulfate B with a D50 of 700 nm, and barium sulfate C with a D50 of 1200 nm, and the weight ratio between them is A:B:C = 20-25:60:15-20. The dispersant used for barium sulfate dispersion is sodium hexametaphosphate; the ethyl titanate is industrial grade tetraethyl titanate; the organic alcohol polyether phosphate is an isomeric alcohol polyether phosphate. The water-soluble sodium silicate is industrial-grade water-soluble sodium silicate. The high solar reflectance white pigment prepared therefrom has a high solar reflectance (TSR) of >98% in the 200nm-2500nm wavelength range.

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