A preparation method of nano calcium carbonate for photovoltaic sealant

Abstract

The present invention discloses a preparation method of nano calcium carbonate for photovoltaic sealant. Limestone is calcined to remove impurities to obtain lime, and then the lime is digested, refined and sieved. After adding a dispersant and grinding and dispersing, raw pulp is obtained. A crystal form control agent is added to the raw pulp to obtain Ca(OH)2 raw pulp. The Ca(OH)2 raw pulp is pumped into a stirring carbonization tower, and after adding kiln gas, nano calcium carbonate pulp is obtained. The nano calcium carbonate pulp is added with a compound surface treatment agent to obtain modified calcium carbonate slurry. The modified calcium carbonate slurry is filtered, dried, crushed, classified and packaged to obtain a nano calcium carbonate product special for photovoltaic glue. The beneficial technical effects are as follows: When the nano calcium carbonate is processed and filled with silicone sealant, it is easy to process, has a low viscosity and good dispersibility. The raw materials used in this method are cheap and easy to obtain, the cost is low, the process is simple and feasible, suitable for industrial production, and has good economic and social benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of manufacturing ultra-fine inorganic powder, and particularly to a preparation method of nano-calcium carbonate for photovoltaic sealant. Background Art

[0002] Calcium carbonate is widely used as a filler in industries such as plastics, rubber, coatings, and papermaking due to its excellent quality and low cost. Photovoltaic adhesives are used as bonding and sealing adhesives on the outer frames and junction boxes of solar photovoltaic modules. After use, the photovoltaic adhesives cure at room temperature using the moisture in the air to complete bonding and sealing. Since solar photovoltaic sealants are mainly used outdoors, they must have good weather resistance, good resistance to ultraviolet radiation, yellowing resistance, good bonding ability, good combustion resistance, resistance to mechanical shock, heat durability, and shock resistance.

[0003] The main raw materials of photovoltaic adhesives include dihydroxypolydimethylsiloxane, silicone oil, fillers, coupling agents, and crosslinking agents. Among them, the filler is mainly nano-calcium carbonate. Nano-calcium carbonate on the market is generally treated with fatty acids and oils. Although it has a low oil absorption value and good processing performance, due to the poor heat resistance, weather resistance, ultraviolet resistance, heat resistance, and yellowing resistance of fatty acids and oils, after long-term aging, problems such as a decrease in bonding ability, easy peeling, and powdering will occur.

[0004] Moreover, the original particle size of nano-calcium carbonate is nano-particles, and the finished product is easily agglomerated into large-particle aggregates, resulting in poor dispersibility, thixotropy, strength, and adhesion, which affects the performance of nano-calcium carbonate.

[0005] In summary, the existing technology obviously has inconveniences and defects in actual use, so it is necessary to improve. Summary of the Invention

[0006] Aiming at the above defects, the purpose of the present invention is to provide a preparation method of nano-calcium carbonate for photovoltaic sealant, and the prepared nano-calcium carbonate has properties such as good dispersibility, strength, elongation, bonding ability, weather resistance, damp heat resistance, and durability under natural conditions.

[0007] To achieve the above purpose, the present invention provides a preparation method of nano-calcium carbonate for photovoltaic sealant, including the following steps:

[0008] S1: Select limestone raw materials. The calcium carbonate content of this limestone is ≥97%, the magnesium carbonate is ≤1.2%, and the limestone with a particle size of 4 - 8 cm and anthracite with a particle size of 1 - 3 cm are mixed in a certain proportion and then added to an environmental protection vertical kiln for calcination. The temperature in the high-temperature zone of the environmental protection vertical kiln is controlled at 900°C - 1100°C. The lime activity of the calcined lime is ≥300 mL / 4N-HCl, and the coal ash and impurities in the lime are screened out.

[0009] S2: Add the lime to a digester with high-speed stirring for digestion. Add hot water according to the weight ratio of ash:water = 1:4 - 6 for digestion. After refining and sieving, add a dispersant to the digester and carry out grinding and dispersion to refine the particle size of the raw materials in the digester. When it is detected that the laser particle size distribution of the raw materials reaches a predetermined value, stop grinding to obtain raw slurry.

[0010] S3: Pump the raw slurry into a slurry adjustment tank, adjust the temperature and concentration of the raw slurry, and add a crystal form control agent to obtain Ca(OH)₂ raw slurry.

[0011] S4: Pump the adjusted Ca(OH)₂ raw slurry into a stirring carbonization tower with high-speed shearing, and introduce purified kiln gas. When carbonization reaches pH ≤ 7.5, detect the particle size of the primary nano-calcium carbonate slurry, turn on the circulating emulsifier for grinding and stirring to refine the nano-calcium carbonate particles. When it is detected that the laser particle size reaches the required particle size, introduce kiln gas for the second time. When pH ≤ 7, stop carbonization. Pump the obtained nano-calcium carbonate slurry into a surface treatment tank and detect the specific surface area of the nano-calcium carbonate slurry.

[0012] S5: Heat the nano-calcium carbonate slurry to 70 - 90°C for standby; add a compound surface treatment agent to the slurry and stir at high speed for 60 - 120 min to obtain a modified calcium carbonate slurry.

[0013] S6: Press-filter, dry, crush, classify and package the modified calcium carbonate slurry to obtain the nano-calcium carbonate product special for photovoltaic glue.

[0014] Furthermore, in step S2, the dispersant is a polyoxyethylene-styrene high molecular polymer dispersant. The dosage of the dispersant is 0.1 - 0.5% of the dry basis mass of calcium hydroxide in the slurry. The dispersant assists the digester to grind and disperse the raw materials in the digester to refine the particle size of the raw slurry. The dispersant can reduce the viscosity during grinding, improve the efficiency during grinding, have good gloss, excellent water resistance and low foaming property.

[0015] Further, in step S4, the circulating emulsifier is equipped with multiple sets of closely fitting stators and rotors. The rotor rotates at a high speed driven by a motor, generating a strong axial suction force to suck the material into the cavity, dispersing, shearing, and emulsifying the material in the shortest time. The particle size distribution range also becomes significantly narrower. It can be cyclically ground and dispersed as needed. When the detected particle size reaches the required value, the grinding stops.

[0016] Further, the measurement method of laser particle size is as follows: Take 2.0 g to 4.0 g of the sample. If the measured material is a slurry, calculate the solid content. Add about 400 mL of water to the sample, add 2 mL of sodium hexametaphosphate to the 200 g / L sample solution, and after ultrasonic treatment of the solution for 3 minutes, add it to the laser particle size analyzer for measurement. The particle size of Ca(OH)2 after refining is usually D50 (median diameter) = 3 μm to 6 μm, D97 (equivalent maximum diameter) = 12 μm to 25 μm. After grinding and dispersion, reaching the predetermined value means D50 ≤ 2 μm, D97 ≤ 10 μm. If D50 > 2 μm and D97 > 10 μm, it indicates that the particle size of Ca(OH)2 is relatively coarse and there are large agglomerated particles. If directly carbonized, it may cause the nano calcium carbonate to wrap the easily agglomerated Ca(OH)2, forming calcium carbonate on the outside and the core still being Ca(OH)2 on the inside, resulting in poor stability of the later product.

[0017] Further, in step S3, adjust the temperature of the raw slurry to 15°C to 30°C, and adjust the concentration of the raw slurry to a mass percentage concentration, with the concentration adjusted to 5% to 12%.

[0018] Further, in step S3, the crystal form control agent includes organic polyols and sulfates. The dosage of organic polyols is 0.5% - 3% of the dry basis amount of Ca(OH)2; the dosage of sulfates is 0.5% - 3% of the dry basis amount of Ca(OH)2.

[0019] Further, in step S4, introduce kiln gas for the second time. The concentration of CO2 in the kiln gas is 25% - 40%. The particle size of the primary nano calcium carbonate slurry is D50 = 2 μm - 5 μm, D97 = 7 μm - 16 μm. Start the circulating emulsifier for grinding and stirring; when the detected laser particle size reaches the required particle size D50 ≤ 1.0 μm, D97 ≤ 6 μm, introduce kiln gas for the second time.

[0020] Further, the organic polyol is one or more of dibromoneopentyl glycol, dibromobutylene glycol, brominated polyether diol, brominated polyester diol, and tetrabromobisphenol A bis(hydroxyethoxy) ether; the sulfate is one or more of zinc sulfate, zinc chloride, zinc nitrate, and zinc dihydrogen phosphate.

[0021] Further, in step S5, the surface treatment agent includes high melting point fatty acid salts, PEG-polydimethylsiloxane, and water-soluble silane coupling agents.

[0022] The melting point of the high melting point fatty acid salt is ≥ 145 °C, and it has good thermal stability, dispersibility and can reduce the viscosity of nano calcium carbonate. The high melting point fatty acid salt is one or more of calcium stearate, barium stearate, cadmium stearate, aluminum stearate, zinc stearate, barium stearate, lanthanum stearate, lead stearate, cerium stearate, calcium hydroxystearate, zinc hydroxystearate, calcium arachidate, zinc arachidate, calcium behenate, zinc behenate, zinc ricinoleate and cadmium behenate. The dosage of the high melting point fatty acid salt is 1% - 4% of the nano calcium carbonate;

[0023] PEG - polydimethylsiloxane is an emulsifier with an HLB value, which can disperse high melting point fatty acids and silane coupling agents. PEG - polydimethylsiloxane is one or more of PEG-8 polydimethylsiloxane, PEG-10 polydimethylsiloxane, PEG-12 polydimethylsiloxane. The dosage of PEG - polydimethylsiloxane is 0.5% - 2% of the nano calcium carbonate;

[0024] The water-soluble silane coupling agent molecule contains an organic functional group and a methoxy group that can react with nano calcium carbonate. The water-soluble silane coupling agent is one or several of mercapto-containing silane organosilicon oligomer X-41-1805, mercapto-containing silane organosilicon oligomer X-41-1810, epoxy group-containing organosilicon oligomer coupling agent KR-516, epoxy group-containing organosilicon oligomer coupling agent KR-517. The dosage of the water-soluble silane coupling agent is 1% - 3% of the nano calcium carbonate.

[0025] Furthermore, the pH of the nano calcium carbonate is 8 - 10, the moisture content is < 0.5%, the oil absorption value is 20 g DOP / 100 g - 30 g DOP / 100 g, the specific surface area is 30 m 2 / g - 45 m 2 / g, the laser particle size D50 ≤ 1.0 μm, D97 ≤ 10.0 μm, the blue light whiteness ≥ 95%, the hue L value ≥ 94.5, the a value ≤ 0, the b value ≤ 3.2, the blue light whiteness after aging ≥ 93.5%, the hue L value after aging ≥ 93%, the a value ≤ 1, the b value ≤ 4.

[0026] The purpose of the present invention is to provide a preparation method of nano calcium carbonate for photovoltaic sealant. By calcining limestone to remove impurities to obtain lime, then digesting, refining and sieving the lime, adding a dispersant and grinding and dispersing to obtain raw pulp, adding a crystal form control agent to the raw pulp to obtain Ca(OH)2 raw pulp, pumping the Ca(OH)2 raw pulp into a stirring carbonization tower, adding kiln gas to obtain nano calcium carbonate pulp, adding a compound surface treatment agent to the nano calcium carbonate pulp to obtain a modified calcium carbonate slurry, and after filtering, drying, pulverizing, classifying and packaging the modified calcium carbonate slurry, a nano calcium carbonate product special for photovoltaic glue is obtained.

[0027] The beneficial technical effects of the present invention are as follows: The prepared nano calcium carbonate has a pH of 8 - 10, a moisture content of < 0.5%, an oil absorption value of 20 g DOP / 100 g - 30 g DOP / 100 g, a specific surface area of 30 m 2 / g - 45 m 2 / g, a laser particle size with D50 ≤ 1.0 μm, D97 ≤ 10.0 μm, a blue light whiteness ≥ 95%, a hue L value ≥ 94.5, an a value ≤ 0, a b value ≤ 3.2, a blue light whiteness ≥ 93.5% after aging, a hue L value ≥ 93% after aging, an a value ≤ 1, and a b value ≤ 4. When the nano calcium carbonate of the present invention is processed and filled into an organosilicon sealant, it is easy to process, has a low viscosity, good dispersibility, enables the sealant to have good adhesion, strength, and elongation, has good corrosion resistance, good acid and alkali resistance, high antioxidant and anti-aging properties, firmly adheres to the substrate, and does not crack or fall off. The three-component composite surface treatment agent selected in the present invention can make the nano calcium carbonate and the organosilicon sealant have good compatibility, effectively improve the processing performance of the filling system, and have good dispersibility, a low oil absorption value, a low viscosity, strength, elongation, weather resistance, water resistance, and durability. The raw materials used in the method of the present invention are cheap and easily available, the cost is low, the process is simple and feasible, suitable for industrial production, and has good economic and social benefits. Detailed implementation manners

[0028] In order to make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0029] The present invention has improved the preparation method of nano calcium carbonate from the following aspects:

[0030] (1) Control the component content in limestone: Controlling the calcium carbonate and magnesium carbonate content in limestone is beneficial to reducing the magnesium carbonate content in the finished product. Since magnesium carbonate has poor heat resistance, reducing the magnesium carbonate content is beneficial to improving heat resistance.

[0031] (2) Control the activity of lime: Controlling the calcination temperature of limestone is beneficial to improving the activity of lime. The improvement of lime activity is beneficial to generating calcium hydroxide with high reaction activity and small particle size, which is beneficial to reducing the particle size and improving the dispersibility of nano calcium carbonate.

[0032] (3) Grinding and refining calcium hydroxide can significantly increase the reaction rate, reduce the agglomeration particle size of nano calcium carbonate, and improve the strength and durability of nano calcium carbonate.

[0033] (4) Controlling the specific surface area and particle size of the nano-calcium carbonate slurry can prevent the agglomeration of nano-calcium carbonate, improve its dispersibility, and reduce the agglomeration index of nano-calcium carbonate.

[0034] (5) The obtained nano-calcium carbonate is treated with a composite surface treatment agent to improve the reinforcement, compatibility of the silicone sealant using this nano-calcium carbonate as a filler, and obtain products with ideal mechanical properties, heat resistance, moisture and heat resistance, weather resistance, and durability.

[0035] To verify the influence of the above improvement points on the preparation of nano-calcium carbonate, the following examples are set:

[0036] Example 1, preparing nano-calcium carbonate for photovoltaic glue using the following steps:

[0037] Step 1: Select high-quality raw material limestone, control the calcium carbonate content of the limestone raw material to be 98%, the magnesium carbonate content to be 0.9%, the lump diameter of the limestone to be 4 - 8 cm, the lump diameter of the anthracite to be 1 - 3 cm. The limestone and anthracite are added to an environmental protection vertical kiln for calcination at a ratio of 1:0.09. Control the calcination temperature in the high-temperature zone to be 950 °C. The activity of the calcined lime is 320 mL / 4N-HCl. Sieve out the coal ash and impurities in the lime, and add it to a digestive machine with high-speed stirring for digestion. During digestion, the weight ratio of ash to water is 1:5, and the temperature of the added water is 50 °C. After digestion, refine it and pass through a 250-mesh sieve. At this time, the particle size of the raw slurry is detected as D50 = 4.21 μm, D97 = 15.51 μm. Add a polyoxyethylene-styrene polymer dispersant with a dry basis amount of 0.15% of the raw slurry, and use a pipeline emulsifier to circulate and grind the raw slurry for dispersion to refine the particle size of the raw slurry. When the particle size of the raw slurry reaches D50 = 1.81 μm, D97 = 8.53 μm, stop grinding;

[0038] Step 2: Pump the raw slurry into a slurry adjustment tank, adjust the temperature of the raw slurry to 25 °C and the mass percentage concentration to 10.2%. Use dibromobutylene glycol and zinc sulfate as crystal form control agents, and both are added at 1% of the Ca(OH)2 dry basis content to obtain the adjusted Ca(OH)2 raw slurry;

[0039] Step 3: Pump the adjusted fresh Ca(OH)2 slurry into a stirring carbonization tower with high-speed shearing, and introduce purified kiln gas with a CO2 concentration of 30%. When the carbonization reaches pH = 7.2, measure the particle size of the primary nano calcium carbonate slurry. The particle sizes are D50 = 2.84 μm and D97 = 9.50 μm. Then start the circulating emulsifier for grinding and stirring to refine the particle size of the nano calcium carbonate. When the measured particle sizes are D50 = 0.85 μm and D97 = 5.42 μm, stop the grinding. At this time, pH = 9.5. Then introduce the kiln gas for the second time. When pH = 7.0, stop the carbonization. Pump the slurry into the surface treatment tank to obtain calcium carbonate slurry, and measure the specific surface area of the calcium carbonate slurry = 35.32 m 2 / g;

[0040] Step 4: Heat the calcium carbonate slurry with steam to 75 °C for standby; add a compound surface treatment agent to the calcium carbonate slurry. The compound surface treatment agent includes zinc stearate, PEG-10 polydimethylsiloxane, and a mercapto-silane organosilicon oligomer coupling agent X-41-1805. Add zinc stearate at 3% of the dry basis content of calcium carbonate, add PEG-10 polydimethylsiloxane at 1% of the dry basis content of calcium carbonate, and add the mercapto-silane organosilicon oligomer coupling agent X-41-1805 at 1% of the dry basis content of calcium carbonate. Prepare an aqueous solution with a concentration of 15% and a temperature of 85 °C from the calcium carbonate slurry, and stir at high speed for 65 min to obtain a modified calcium carbonate slurry;

[0041] Step 5: Subject the modified calcium carbonate slurry to pressure filtration, drying, crushing, classification, and packaging to obtain a nano calcium carbonate product special for photovoltaic adhesives.

[0042] Comparative Example 1: Other steps are the same as those in Example 1, except that the crystal form control agent added in Step 2 is white sugar, and white sugar is added at 2% of the dry basis content of Ca(OH)2.

[0043] Detect the nano calcium carbonate in Example 1: pH = 8.92, moisture content = 0.38%, oil absorption value = 23.5 g DOP / 100 g, specific surface area = 33.51 m 2 / g, laser particle size D50 = 0.91 μm, D97 = 6.32 μm, blue light whiteness = 96.3%, hue L value = 95.9%, a value = -1.01, b value = 2.82, blue light whiteness after aging = 95.1%, hue L value = 94.7%, a value = -0.88, b value = 3.64.

[0044] Detect the nano calcium carbonate in Comparative Example 1: pH = 8.94, moisture content = 0.38%, oil absorption value = 23.6 g DOP / 100 g, specific surface area = 33.60 m 2 / g, laser particle size D50 = 0.89μm, D97 = 6.34μm, blue light whiteness = 95.7%, hue L value = 95.4%, a value = -0.85, b value = 2.94. After aging, blue light whiteness = 92.4%, hue L value = 92.2%, a value = -0.15, b value = 4.88.

[0045] In summary, compared with Comparative Example 1, Example 1 has good anti-aging ability.

[0046] Example 2: The following steps are used to prepare nano-calcium carbonate for photovoltaic adhesives:

[0047] Step 1: Select high-quality raw material limestone, control the calcium carbonate content of the limestone raw material to be 98.2%, the magnesium carbonate content to be 0.8%, the lump diameter of the limestone to be 4 - 8 cm, and the lump diameter of the anthracite to be 1 - 3 cm. The limestone and anthracite are added to an environmental protection vertical kiln for calcination at a ratio of 1:0.092. Control the calcination temperature in the high-temperature zone to be 1000°C. The activity of the calcined lime is 315 mL / 4N-HCl. Sieve out the coal ash and impurities in the lime, and add it to a digestive machine with high-speed stirring for digestion. When digesting, the weight ratio of ash to water is 1:6, and the temperature of the added water is 60°C. After digestion, refine and pass through a 300-mesh sieve. At this time, the particle size of the raw pulp is detected as D50 = 3.94μm, D97 = 14.26μm. Add a polyoxyethylene-styrene polymer dispersant with a dry basis amount of 0.15% of the raw pulp, and use a pipeline emulsifier to circulate and grind and disperse the raw pulp to refine the particle size of the raw pulp. When the particle size of the raw pulp reaches D50 = 1.75μm, D97 = 7.92μm, stop grinding;

[0048] Step 2: Pump the raw pulp into a pulp adjustment tank, adjust the temperature of the raw pulp to 26°C and the mass percentage concentration to 9.8%. Use dibromobutylene glycol and zinc sulfate as crystal form control agents. Add dibromobutylene glycol at 1.2% of the Ca(OH)2 dry basis content, and add zinc sulfate at 1.5% of the Ca(OH)2 dry basis content to obtain the adjusted Ca(OH)2 raw pulp;

[0049] Step 3: Pump the adjusted Ca(OH)2 raw pulp into a stirring carbonization tower with high-speed shearing, and introduce purified kiln gas. The CO2 concentration in the kiln gas is 32%. When carbonization reaches pH = 7.3, detect the particle size of the original nano-calcium carbonate pulp. The particle size is D50 = 2.62μm, D97 = 9.46μm. Start the circulating emulsifier for grinding and stirring to refine the particle size of the nano-calcium carbonate. When the detected particle size is D50 = 0.75μm, D97 = 4.94μm, stop grinding. At this time, pH = 10.2. Then introduce the kiln gas for the second time. When pH = 7.0, stop carbonization. Pump the pulp into a surface treatment tank to obtain calcium carbonate slurry, and detect the specific surface area of the calcium carbonate slurry = 38.40m2 / g;

[0050] Step 4: Pass the calcium carbonate slurry into steam and heat it to 75 °C for standby; add a surface treatment agent to the calcium carbonate slurry. The surface treatment agent includes calcium stearate, barium stearate, zinc stearate, PEG-8 polydimethylsiloxane, and an epoxy-group-containing organosilicon oligomer coupling agent KR-517. Add calcium stearate at 2% of the dry basis content of calcium carbonate, add barium stearate at 1% of the dry basis content of calcium carbonate, add zinc stearate at 0.5% of the dry basis content of calcium carbonate, add PEG-8 polydimethylsiloxane at 1% of the dry basis content of calcium carbonate, and add the epoxy-group-containing organosilicon oligomer coupling agent KR-517 at 1% of the dry basis content of calcium carbonate. Prepare the calcium carbonate slurry into an aqueous solution with a concentration of 10% and a temperature of 85 °C, and stir at high speed for 75 min to obtain a modified calcium carbonate slurry;

[0051] Step 5: Subject the modified calcium carbonate slurry to pressure filtration, drying, pulverization, classification, and packaging to obtain a nano calcium carbonate product special for photovoltaic glue.

[0052] Comparative Example 2, other steps are the same as those in Example 2, the difference is that in Step 4, the surface treatment agent is sodium stearate, and sodium stearate is added at 5.5% of the dry basis content of calcium carbonate. Prepare the calcium carbonate slurry into an aqueous solution with a concentration of 10% and a temperature of 85 °C, and stir at high speed for 75 min to obtain a modified calcium carbonate slurry.

[0053] Detect the nano calcium carbonate in Example 2: pH = 8.78, moisture content = 0.36%, oil absorption value = 26.5 g DOP / 100 g, specific surface area = 35.24 m 2 / g, laser particle size D50 = 0.82 μm, D97 = 6.51 μm, blue light whiteness = 96.2%, hue L value = 95.7%, a value = -0.97, b value = 2.85, blue light whiteness after aging = 95.0%, hue L value = 94.8%, a value = -0.82, b value = 3.67.

[0054] Detect the nano calcium carbonate in Comparative Example 2: pH = 9.12, moisture content = 0.38%, oil absorption value = 26.8 g DOP / 100 g, specific surface area = 35.42 m 2 / g, laser particle size D50 = 0.86 μm, D97 = 6.63 μm, blue light whiteness = 95.7%, hue L value = 95.4%, a value = -0.84, b value = 2.97, blue light whiteness after aging = 91.7%, hue L value = 91.5%, a value = 0.38, b value = 5.82.

[0055] In summary, compared with Comparative Example 2, Example 2 has good anti-aging properties, the prepared nano calcium carbonate has small particle size, low oil absorption value, and the pH is more neutral.

[0056] Example 3. The special nano calcium carbonate for photovoltaic adhesive was prepared by the following steps:

[0057] Step 1: Select high-quality raw material limestone, and control the calcium carbonate content of the limestone raw material to be 98.3%, the magnesium carbonate content to be 0.7%, the lump diameter of the limestone to be 4 - 8 cm, and the lump diameter of the anthracite to be 1 - 3 cm. The limestone and anthracite are added to an environmental vertical kiln for calcination at a ratio of 1:0.093. Control the calcination temperature in the high-temperature zone to be 1000 °C. The activity of the calcined lime is 325 mL / 4N-HCl. Sieve out the coal ash and impurities in the lime, and add it to a digestive machine with high-speed stirring for digestion. During digestion, the weight ratio of ash to water is 1:6, and the temperature of the added water is 60 °C. After digestion, carry out refining and pass through a 300-mesh sieve. At this time, the particle size of the raw pulp is detected as D50 = 3.54 μm and D97 = 13.5 μm. Add a polyoxyethylene-styrene polymer dispersant accounting for 0.15% of the dry basis of the raw pulp, and use a pipeline emulsifier to circulate and grind the raw pulp for dispersion to refine the particle size of the raw pulp. When the particle size of the raw pulp reaches D50 = 1.64 μm and D97 = 7.65 μm, stop grinding;

[0058] Step 2: Pump the raw pulp into a pulp adjustment tank, adjust the temperature of the raw pulp to 27 °C and the mass percentage concentration to 9.5%. Use tetrabromobisphenol A bis(2-hydroxyethoxy) ether and zinc sulfate as crystal form control agents. Add tetrabromobisphenol A bis(2-hydroxyethoxy) ether accounting for 1.2% of the Ca(OH)2 dry basis content, and add zinc sulfate accounting for 2.0% of the Ca(OH)2 dry basis content;

[0059] Step 3: Pump the adjusted Ca(OH)2 raw pulp into a stirring carbonization tower with high-speed shearing, and introduce purified kiln gas. The CO2 concentration in the kiln gas is 32%. When carbonization reaches pH = 7.1, detect the particle size of the primary nano calcium carbonate pulp. The particle size is D50 = 2.42 μm and D97 = 8.63 μm. Start the circulating emulsifier for grinding and stirring to refine the particle size of the nano calcium carbonate. When the detected particle size is D50 = 0.62 μm and D97 = 4.8 μm, stop grinding. At this time, pH = 10.5. Then introduce the kiln gas for the second time. When pH = 7.0, stop carbonization. Pump the pulp into a surface treatment tank to obtain a calcium carbonate slurry, and detect the specific surface area of the calcium carbonate slurry = 39.85 m 2 / g;

[0060] Step 4: Pass the calcium carbonate slurry into steam and heat it to 75°C for standby; add a surface treatment agent to the calcium carbonate slurry. The surface treatment agent includes barium stearate, zinc stearate, PEG-12 polydimethylsiloxane, and epoxy group organosilicon oligomer coupling agent KR-516. Add barium stearate at 2% of the dry basis content of calcium carbonate, add zinc stearate at 1.5% of the dry basis content of calcium carbonate, add PEG-12 polydimethylsiloxane at 1% of the dry basis content of calcium carbonate, and add epoxy group organosilicon oligomer coupling agent KR-516 at 1% of the dry basis content of calcium carbonate. Prepare the calcium carbonate slurry into an aqueous solution with a concentration of 10% and a temperature of 85°C, and stir at high speed for 70 min to obtain a modified calcium carbonate slurry;

[0061] Step 5: Subject the modified calcium carbonate slurry to pressure filtration, drying, pulverization, classification, and packaging to obtain a nano calcium carbonate product special for photovoltaic adhesives.

[0062] Comparative Example 3: Other steps are the same as those in Example 3, except that in Step 3, the circulation emulsifier is not turned on for grinding and stirring. Detect the particle size of the raw nano calcium carbonate slurry, D50 = 2.42 μm, D97 = 8.63 μm. Pass the kiln gas again, and stop carbonization when pH = 7.0. Pump the slurry into the surface treatment tank, and detect the specific surface area of the nano calcium carbonate slurry = 39.85 m 2 / g; in Step 4, the surface treatment agent is soap granule. Add soap granule at 5.5% of the dry basis content of calcium carbonate, prepare the calcium carbonate slurry into a concentration of 12%, and stir at high speed for 70 min to obtain a modified calcium carbonate slurry.

[0063] Detect the nano calcium carbonate in Example 3: pH = 8.98, moisture content = 0.36%, oil absorption value = 25.3 g DOP / 100 g, specific surface area = 37.65 m 2 / g, laser particle size D50 = 0.69 μm, D97 = 6.98 μm, blue light whiteness = 96.0%, hue L value = 95.5%, a value = -0.90, b value = 2.90, blue light whiteness after aging = 94.9%, hue L value = 94.7%, a value = -0.70, b value = 3.65.

[0064] Detect the nano calcium carbonate in Comparative Example 3: pH = 8.98, moisture content = 0.36%, oil absorption value = 25.4 g DOP / 100 g, specific surface area = 37.26 m 2 / g, laser particle size D50 = 2.89 μm, D97 = 12.31 μm, blue light whiteness = 95.5%, hue L value = 95.3%, a value = -0.80, b value = 2.96, blue light whiteness after aging = 90.2%, hue L value = 90.0%, a value = 0.79, b value = 6.84.

[0065] In summary, compared with Comparative Example 3, Example 3 has good anti-aging properties, and the prepared nano-calcium carbonate has small particle size, beautiful and delicate appearance, and no coarse particles.

[0066] Comprehensively comparing the data of the above examples and comparative examples, the data are as follows in the table:

[0067]

[0068] After the comparative experiments of the above examples and through comprehensive data analysis, a preparation method of nano-calcium carbonate for photovoltaic sealant is obtained, including the following steps:

[0069] S1: Select limestone raw materials. The calcium carbonate content of the limestone is ≥97%, the magnesium carbonate is ≤1.2%. Limestone with a particle size of 4 - 8 cm and anthracite with a particle size of 1 - 3 cm are mixed in a certain proportion and then added to an environmental vertical kiln for calcination. The temperature in the high-temperature zone of the environmental vertical kiln is controlled at 900°C - 1100°C. The activity of the calcined lime is ≥300 mL / 4N-HCl, and the coal ash and impurities in the lime are sieved out;

[0070] S2: Add the lime to a digestive machine with high-speed stirring for digestion. Hot water is added according to the weight ratio of ash: water = 1:4 - 6 for digestion. After refining and sieving, a dispersant is added to the digestive machine, and grinding and dispersion are carried out to refine the particle size of the raw materials in the digestive machine. When the laser particle size distribution of the raw materials reaches a predetermined value, stop grinding to obtain raw pulp;

[0071] S3: Pump the raw pulp into a slurry adjustment tank, adjust the temperature and concentration of the raw pulp, and add a crystal form control agent to obtain Ca(OH)2 raw pulp;

[0072] S4: Pump the adjusted Ca(OH)2 raw pulp into a stirring carbonization tower with high-speed shearing, and introduce purified kiln gas. When the carbonization reaches pH ≤ 7.5, detect the particle size of the primary nano-calcium carbonate slurry, start the circulating emulsifier for grinding and stirring to refine the nano-calcium carbonate particles. When the laser particle size reaches the required particle size, introduce the kiln gas for the second time. When pH ≤ 7, stop carbonization. Pump the obtained nano-calcium carbonate slurry into a surface treatment tank, and detect the specific surface area of the nano-calcium carbonate slurry;

[0073] S5: Heat the nano-calcium carbonate slurry to 70 - 90°C for standby; add a compound surface treatment agent to the slurry and stir at high speed for 60 - 120 min to obtain a modified calcium carbonate slurry;

[0074] S6: Press-filter, dry, crush, classify and package the modified calcium carbonate slurry to obtain the nano-calcium carbonate product special for photovoltaic glue.

[0075] In the above step S2, the dispersant is a polyoxyethylene-styrene high molecular polymer dispersant, and the dosage of the dispersant is 0.1% to 0.5% of the dry basis mass of calcium hydroxide in the slurry. If the dosage is less than 0.1%, the effect of viscosity reduction is not significantly improved, and thickening may occur during the grinding process. If the dosage is higher than 0.5%, it is feared that foaming will occur during carbonization, causing the slurry to overflow from the carbonization tower, and at the same time, the cost is high. The dispersant assists the digester to grind and disperse the raw materials in the digester, making the particle size of the raw pulp finer. The dispersant can reduce the viscosity during grinding, improve the grinding efficiency, have good gloss, excellent water resistance, and low foaming property.

[0076] In the above step S4, the circulating emulsifier is equipped with multiple groups of closely fitting stators and rotors. The rotor rotates at a high speed driven by a motor, generating a strong axial suction force to suck the material into the cavity, and dispersing, shearing, and emulsifying the material in the shortest time. The particle size distribution range also becomes significantly narrower, and it can be cyclically ground and dispersed as needed. When the detected particle size reaches the required value, the grinding is stopped. The grinding equipment for grinding and dispersing the raw pulp to make the particle size of the raw pulp finer can be a medium grinding disperser, a device for grinding Ca(OH)2 by adding grinding beads such as glass beads, alumina, zirconia, agate, etc., such as: sand mill, peeling machine, stirring mill, ball mill, vibration mill, etc.; it can also be a medium-free grinding disperser, such as: shear emulsifier, colloid mill, high-pressure homogenizer, etc.

[0077] The measurement method of the laser particle size in the preparation method is as follows: Take 2.0 g to 4.0 g of the sample. If the measured substance is a slurry, calculate the solid content. Add about 400 mL of water to the sample, add 2 mL of sodium hexametaphosphate to the 200 g / L sample solution, and after ultrasonic treatment of the solution for 3 minutes, add it to the laser particle size analyzer for determination. The particle size of Ca(OH)2 after refining is usually D50 (median diameter) = 3 μm to 6 μm, D97 (equivalent maximum diameter) = 12 μm to 25 μm. After grinding and dispersing to reach the predetermined value, it means D50 ≤ 2 μm, D97 ≤ 10 μm. If D50 > 2 μm and D97 > 10 μm, it means that the particle size of Ca(OH)2 is relatively coarse and there are large agglomerated particle sizes. If directly carbonized, it may cause the nano calcium carbonate to wrap the easily agglomerated Ca(OH)2, forming calcium carbonate on the outside and the core still being Ca(OH)2 on the inside, resulting in poor stability of the later product.

[0078] In the above step S3, adjust the temperature of the raw pulp to 15°C to 30°C. If the temperature is too low, the freezing cost is too high, and at the same time, the particle size is unstable. If the temperature is too high, it is difficult to generate nano calcium carbonate with a smaller particle size; adjust the concentration of the raw pulp to a mass percentage concentration, and the concentration is adjusted to 5% to 12%. If it is lower than 5%, the industrial production cost is higher. If it is higher than 12%, it is difficult to generate nano calcium carbonate with a smaller particle size.

[0079] The crystal form control agent includes organic polyols and sulfates. The dosage of the organic polyol is 0.5% - 3% of the dry basis amount of Ca(OH)₂; the organic polyol is a halogen-containing polyol, such as one or more of dibromoneopentyl glycol, dibromobutylene glycol, bromine-containing polyether diol, bromine-containing polyester diol, and tetrabromobisphenol A bis(hydroxyethoxy) ether; the halogen-containing organic polyol can increase the solubility of calcium hydroxide, reduce the particle size of the produced nano-calcium carbonate, and improve the thermal stability and flame retardancy in the final dried product. At the same time, it can improve the bonding strength, flexibility, water resistance, heat resistance, and flame retardancy performance.

[0080] The dosage of the sulfate is 0.5% - 3% of the dry basis amount of Ca(OH)₂; the sulfate is one or more of zinc sulfate, zinc chloride, zinc nitrate, and zinc dihydrogen phosphate, and preferably zinc sulfate monohydrate or zinc sulfate heptahydrate. Zinc sulfate can react with Ca(OH)₂ to form CaSO₄ whiskers and Zn(OH)₂, making CaCO₃ form a fine chain-like structure and increasing the specific surface area. At the same time, after drying, ZnO is formed. Zinc oxide is an excellent heat-resistant agent, which can coat the nano-calcium carbonate and improve the heat resistance, weather resistance, and mildew resistance of the nano-calcium carbonate.

[0081] In the above step S4, when the kiln gas is introduced for the second time, the concentration of CO₂ in the kiln gas is 25% - 40%. If it is lower than 25%, it is difficult to obtain fine nano-calcium carbonate, and if it is higher than 40%, it is difficult to achieve industrial production. The particle size of the primary nano-calcium carbonate slurry is D50 = 2μm - 5μm, D97 = 7μm - 16μm. If directly activated, agglomerated nano-calcium carbonate will be obtained, and the performance of the small particle size of the nano-calcium carbonate cannot be fully exerted. Turn on the circulating emulsifier for grinding and stirring; when the detected laser particle size reaches the required particle size D50 ≤ 1.0μm, D97 ≤ 6μm, introduce the kiln gas for the second time. If the particle size is too large, it may cause the strength, dispersibility, etc. of the nano-calcium carbonate to deteriorate. The purpose of introducing the kiln gas for the second time is that after the nano-calcium carbonate slurry is ground, the particles become finer, and the wrapped Ca(OH)₂ particles are exposed. At this time, the pH value of the slurry rises to 8 - 12. Introducing the kiln gas containing CO₂ at this time is beneficial to the formation of pure nano-calcium carbonate, preventing agglomeration, and at the same time reducing the pH of the system.

[0082] In the above step S5, the surface treatment agent includes high melting point fatty acid salts, PEG-polydimethylsiloxane, and water-soluble silane coupling agents. The melting point of the high melting point fatty acid salts is ≥145°C, and they have good thermal stability, dispersibility, and can reduce the viscosity of nano calcium carbonate. The high melting point fatty acid salts are one or more of calcium stearate, barium stearate, cadmium stearate, aluminum stearate, zinc stearate, barium stearate, lanthanum stearate, lead stearate, cerium stearate, calcium hydroxystearate, zinc hydroxystearate, calcium arachidate, zinc arachidate, calcium behenate, zinc behenate, zinc ricinoleate, and cadmium behenate. The dosage of the high melting point fatty acid salts is 1% - 4% of the nano calcium carbonate. If the dosage is too small, it is not enough to reduce the viscosity. If the dosage is too large, the excess fatty acid salts are likely to desorb, which may cause poor adhesion.

[0083] PEG-polydimethylsiloxane is an emulsifier with an HLB value, which can disperse high melting point fatty acids and silane coupling agents. PEG-polydimethylsiloxane is one or more of PEG-8 polydimethylsiloxane, PEG-10 polydimethylsiloxane, and PEG-12 polydimethylsiloxane. The dosage of PEG-polydimethylsiloxane is 0.5% - 2% of the nano calcium carbonate. If the dosage is too small, it is not enough to disperse the fatty acid salts and coupling agents. If the dosage is too large, the cost is too high.

[0084] The water-soluble silane coupling agent molecule contains organic functional groups and methoxy groups that can react with nano calcium carbonate. The water-soluble silane coupling agent is one or several of mercapto group-containing silane organosilicon oligomer X-41-1805, mercapto group-containing silane organosilicon oligomer X-41-1810, epoxy group-containing organosilicon oligomer coupling agent KR-516, and epoxy group-containing organosilicon oligomer coupling agent KR-517. The dosage of the water-soluble silane coupling agent is 1% - 3% of the nano calcium carbonate. If the dosage is too small, it is not enough to provide sufficient strength and weather resistance. If it is too much, the cost increases too much.

[0085] By compounding the above three components, good compatibility can be achieved between nano calcium carbonate and silicone sealant, effectively improving the processing performance of the filling system, and having good dispersibility, low oil absorption value, low viscosity, strength, elongation at break, weather resistance, water resistance, and durability.

[0086] In the examples, the specific surface area is the value determined according to the BET (Brunauer Emmett-Teller) method, and the surface of the powder can be calculated from the nitrogen isotherm measured at the boiling point of liquid nitrogen. The method refers to the determination of specific surface area in 3.25 of the analysis method of calcium carbonate in GB / T19281-2014. The specific surface area of the slurry of the nano calcium carbonate is preferably 30m 2 / g to 45m 2 / g. When the specific surface area is greater than 45m 2 / g, indicating that the original particle size of the nano calcium carbonate is small, prone to agglomeration, and the nano calcium carbonate with a small particle size has more porosity between particles, so producing sealant is likely to cause high viscosity of the rubber compound and difficult processing; when the specific surface area is less than 30m 2 / g, indicating that the original particle size of the nano calcium carbonate is large, which may affect the strength of the sealant; after surface treatment, the coating treatment agent of the nano calcium carbonate fills a small amount of pores, so the specific surface area is reduced by 5%-10%.

[0087] Through a preparation method of nano calcium carbonate for photovoltaic sealant, the prepared nano calcium carbonate has a pH of 8-10, a moisture content of <0.5%, an oil absorption value of 20g DOP / 100g - 30g DOP / 100g, a specific surface area of 30m 2 / g - 45m 2 / g, the laser particle size means D50 ≤ 1.0μm, D97 ≤ 10.0μm, the blue light whiteness ≥ 95%, the hue L value ≥ 94.5, the a value ≤ 0, the b value ≤ 3.2, the blue light whiteness after aging ≥ 93.5%, the hue L value after aging ≥ 93%, the a value ≤ 1, the b value ≤ 4. The aging here is detected after the powder is baked in a constant temperature drying oven at 180°C for 5 hours. The L value is the brightness, and the larger the L value, the greater the brightness and whiteness. The positive a value indicates a red phase, and the negative value indicates a green phase; the positive b value indicates a yellow phase, and the negative value indicates a blue phase. After oven aging, the smaller the color change range, the more heat-resistant the powder is.

[0088] To verify the performance of the photovoltaic glue prepared from the nano calcium carbonate prepared in the above examples and comparative examples, the following several application examples are set up.

[0089] Application Example 1: Using the nano calcium carbonate obtained in Example 1 as a filler, an organosilicon photovoltaic glue is prepared through the following steps:

[0090] Step 1: Add 100 parts of α,ω-dihydroxypolydimethylsiloxane with a viscosity of 20Pa·S, 90 parts of nano calcium carbonate, 5 parts of fumed silica, and 5 parts of silicone oil with a viscosity of 0.35Pa·S in proportion to a biaxial planetary power mixer. At a high temperature of 130°C, evacuate, the vacuum degree is 0.09Mpa, stir for 2 hours, and cool to obtain the base material.

[0091] Step 2: Add 8 parts of methyltrimethoxysilane, 4 parts of acetylacetonate chelate of isopropyl titanate, 2 parts of KH550 coupling agent, and 2 parts of KH560 coupling agent to the base material. At room temperature, evacuate to a vacuum degree of 0.09 Mpa, stir for 1 hour, and then cool to obtain the silicone photovoltaic adhesive. Perform performance tests on this silicone photovoltaic adhesive. Among them, the appearance has very good dispersion, the surface drying time is 15 min, the tensile strength is 1.55 MPa, the Shore hardness is 38 HA, the elongation at break is 480%, the bond failure rate is 0%. After experiencing a 1000-hour damp heat environment, the tensile strength is 1.32 MPa, the elongation at break is 390%, the bond failure rate is 0%, and the discoloration situation is 1.

[0092] Application Example 2: Using the nano-calcium carbonate prepared in Comparative Example 1 as the filler, prepare the silicone photovoltaic adhesive using the same steps as in Application Example 1. Perform performance tests on this silicone photovoltaic adhesive. Among them, the appearance has very good dispersion, the surface drying time is 15 min, the tensile strength is 1.35 MPa, the Shore hardness is 40 HA, the elongation at break is 445%, the bond failure rate is 0%. After experiencing a 1000-hour damp heat environment, the tensile strength is 1.15 MPa, the elongation at break is 280%, the bond failure rate is 90%, and the discoloration situation is 3.

[0093] Application Example 3: Using the nano-calcium carbonate prepared in Example 2 as the filler, prepare the silicone photovoltaic adhesive using the same steps as in Application Example 1. Perform performance tests on this silicone photovoltaic adhesive. Among them, the appearance has very good dispersion, the surface drying time is 14 min, the tensile strength is 1.62 MPa, the Shore hardness is 39 HA, the elongation at break is 520%, the bond failure rate is 0%. After experiencing a 1000-hour damp heat environment, the tensile strength is 1.37 MPa, the elongation at break is 428%, the bond failure rate is 0%, and the discoloration situation is 1.

[0094] Application Example 4: Using the nano-calcium carbonate prepared in Comparative Example 2 as the filler, prepare the silicone photovoltaic adhesive using the same steps as in Application Example 1. Perform performance tests on this silicone photovoltaic adhesive. Among them, the appearance has very good dispersion, the surface drying time is 16 min, the tensile strength is 1.38 MPa, the Shore hardness is 41 HA, the elongation at break is 450%, the bond failure rate is 5%. After experiencing a 1000-hour damp heat environment, the tensile strength is 0.93 MPa, the elongation at break is 270%, the bond failure rate is 70%, and the discoloration situation is 3.

[0095] Application Example 5: Using the nano-calcium carbonate prepared in Example 3 as the filler, prepare the silicone photovoltaic adhesive using the same steps as in Application Example 1. Perform performance tests on this silicone photovoltaic adhesive. Among them, the appearance has very good dispersion, the surface drying time is 15 min, the tensile strength is 1.66 MPa, the Shore hardness is 40 HA, the elongation at break is 510%, the bond failure rate is 0%. After experiencing a 1000-hour damp heat environment, the tensile strength is 1.39 MPa, the elongation at break is 450%, the bond failure rate is 0%, and the discoloration situation is 1.

[0096] Application Example 6: Using the nano calcium carbonate prepared in Comparative Example 3 as a filler, an organosilicon photovoltaic adhesive was prepared using the same steps as in Application Example 1. Performance tests were conducted on this organosilicon photovoltaic adhesive. The appearance had good dispersion, the surface drying time was 18 minutes, the tensile strength was 1.10 MPa, the Shore hardness was 42 HA, the elongation at break was 380%, the bond failure rate was 25%. After experiencing a damp heat environment for 1000 hours, the tensile strength was 0.76 MPa, the elongation at break was 210%, the bond failure rate was 100%, and the discoloration was 5.

[0097] In the above application examples, the organosilicon photovoltaic adhesive using the nano calcium carbonate prepared in the comparative example as a filler had poor strength, poor elongation at break, a large bond failure area, and deep discoloration. While the organosilicon photovoltaic adhesive using the nano calcium carbonate prepared in the examples of the present invention had excellent weather resistance, anti-aging property, anti-yellowing property, and strong bonding performance. In order to more clearly compare the characteristics of the photovoltaic adhesives in the application examples, the test data was sorted into the following table.

[0098]

[0099] Among them, for the surface drying time, Shore hardness, bond failure rate, tensile bond strength, and elongation at break, aluminum alloy and TPE backplane were used as the bonding substrates, and tests were conducted according to GB / T 13477.8 - 2017 "Test Methods for Building Sealants".

[0100] The present invention relates to a preparation method of nano calcium carbonate for photovoltaic sealant. By calcining limestone to remove impurities to obtain lime, then digesting, refining, and sieving the lime, adding a dispersant and grinding and dispersing to obtain raw pulp, adding a crystal form control agent to the raw pulp to obtain Ca(OH)2 raw pulp, pumping the Ca(OH)2 raw pulp into a stirring carbonization tower, adding kiln gas to obtain nano calcium carbonate pulp, adding a compound surface treatment agent to the nano calcium carbonate pulp to obtain a modified calcium carbonate slurry, and after filtering, drying, pulverizing, classifying, and packaging the modified calcium carbonate slurry, a nano calcium carbonate product special for photovoltaic adhesive is obtained.

[0101] In summary, the beneficial effects of the present invention are:

[0102] (1) The prepared nano calcium carbonate has a pH of 8 - 10, a moisture content of < 0.5%, an oil absorption value of 20 g DOP / 100 g - 30 g DOP / 100 g, a specific surface area of 30 m 2 / g - 45 m 2 / g, the laser particle size index D50 ≤ 1.0 μm, D97 ≤ 10.0 μm, the blue light whiteness ≥ 95%, the hue L value ≥ 94.5, the a value ≤ 0, the b value ≤ 3.2, the blue light whiteness after aging ≥ 93.5%, the hue L value after aging ≥ 93%, the a value ≤ 1, the b value ≤ 4.

[0103] (2)When the nano calcium carbonate of the present invention is processed and filled with the silicone sealant, it is easy to process, has a low viscosity, good dispersibility, enables the sealant to have good adhesion, strength, elongation rate, good anti-corrosion performance, good acid and alkali resistance, high antioxidant and anti-aging performance, firmly adheres to the substrate, and does not crack or fall off.

[0104] (3)The three-component composite surface treatment agent selected in the present invention can make the nano calcium carbonate and the silicone sealant have good compatibility, effectively improve the processing performance of the filling system, and have good dispersibility, low oil absorption value, low viscosity, strength, elongation rate, weather resistance, water resistance and durability.

[0105] (4)The raw materials used in the method of the present invention are cheap and easily available, the cost is low, the process is simple and feasible, suitable for industrial production, and has good economic and social benefits.

[0106] Of course, the present invention can also have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and deformations according to the present invention, but these corresponding changes and deformations should all fall within the protection scope of the appended claims of the present invention.

Claims

1. A preparation method of nano calcium carbonate for photovoltaic sealant, characterized in that, It includes the following steps: S1: Select limestone raw materials. The calcium carbonate content of the limestone is ≥97%, the magnesium carbonate is ≤1.2%, and the limestone with a particle size of 4 - 8 cm and anthracite with a particle size of 1 - 3 cm are mixed in a certain proportion and then added to an environmental vertical kiln for calcination. The temperature in the high-temperature zone of the environmental vertical kiln is controlled at 900°C - 1100°C. The lime activity of the calcined lime is ≥300 mL / 4N-HCl, and the coal ash and impurities in the lime are sieved out. S2: Add the lime to a digester with high-speed stirring for digestion. Add hot water according to the weight ratio of ash:water = 1:4 - 6 for digestion. After refining and sieving, add a dispersant to the digester and grind and disperse it to refine the particle size of the raw materials in the digester. When the laser particle size distribution of the raw materials is detected to reach a predetermined value, stop grinding to obtain raw slurry. S3: Pump the raw slurry into a slurry adjustment tank, adjust the temperature and concentration of the raw slurry, and add a crystal form control agent to obtain Ca(OH)2 raw slurry. S4: Pump the adjusted Ca(OH)2 raw slurry into a stirring carbonization tower with high-speed shearing, and introduce purified kiln gas. When the carbonization reaches pH ≤ 7.5, detect the particle size of the primary nano-calcium carbonate slurry, turn on the circulating emulsifier for grinding and stirring to refine the nano-calcium carbonate particles. When the detected laser particle size reaches the required particle size, introduce the kiln gas for the second time. When pH ≤ 7, stop carbonization, pump the obtained nano-calcium carbonate slurry into a surface treatment tank, and detect the specific surface area of the nano-calcium carbonate slurry. S5: Heat the nano-calcium carbonate slurry to 70 - 90°C for standby; add a compound surface treatment agent to the slurry and stir at high speed for 60 - 120 min to obtain a modified calcium carbonate slurry. S6: Press-filter, dry, crush, classify, and package the modified calcium carbonate slurry to obtain a nano-calcium carbonate product special for photovoltaic glue. In step S2, the dispersant is a polyoxyethylene-styrene polymer dispersant, and the dosage of the dispersant is 0.1% - 0.5% of the dry basis mass of calcium hydroxide in the slurry. In step S3, the crystal form control agent includes organic polyols and salts. The dosage of organic polyols is 0.5% - 3% of the dry basis amount of Ca(OH)2; the dosage of salts is 0.5% - 3% of the dry basis amount of Ca(OH)2. In step S5, the surface treatment agent includes high melting point fatty acid salts, PEG-polydimethylsiloxane, and water-soluble silane coupling agents. The melting point of the high melting point fatty acid salt is ≥145°C. The high melting point fatty acid salt is one or more of calcium stearate, barium stearate, cadmium stearate, aluminum stearate, zinc stearate, barium stearate, lanthanum stearate, lead stearate, cerium stearate, calcium hydroxy stearate, zinc hydroxy stearate, calcium arachidate, zinc arachidate, calcium behenate, zinc behenate, zinc ricinoleate, and cadmium behenate. The dosage of the high melting point fatty acid salt is 1% - 4% of the nano-calcium carbonate. PEG-polydimethylsiloxane is an emulsifier with an HLB value. The PEG-polydimethylsiloxane is one or more of PEG-8 polydimethylsiloxane, PEG-10 polydimethylsiloxane, and PEG-12 polydimethylsiloxane. The dosage of PEG-polydimethylsiloxane is 0.5% - 2% of nano calcium carbonate; The water-soluble silane coupling agent is one or several of mercapto-silane organosilicon oligomer X-41-1805, mercapto-silane organosilicon oligomer X-41-1810, epoxy-group-containing organosilicon oligomer coupling agent KR-516, and epoxy-group-containing organosilicon oligomer coupling agent KR-517. The dosage of the water-soluble silane coupling agent is 1% - 3% of nano calcium carbonate.

2. The preparation method of nano calcium carbonate for photovoltaic sealant according to claim 1, characterized in that, In step S4, the circulation emulsifier is equipped with multiple groups of closely fitting stators and rotors. The rotor rotates at a high speed driven by a motor, generating a strong axial suction force to suck the material into the cavity, dispersing, shearing, and emulsifying the material in the shortest time, and the particle size distribution range also becomes significantly narrower. Grind and disperse in a cycle as needed. When the detected particle size reaches the required value, stop grinding.

3. The preparation method of nano calcium carbonate for photovoltaic sealant according to claim 1, characterized in that, The measurement method of laser particle size is as follows: Take 2.0 g - 4.0 g of the sample. If the measured substance is a slurry, calculate the solid content. Add 400 mL of water to the sample, add 2 mL of sodium hexametaphosphate to the 200 g / L sample solution, and after ultrasonic treatment of the solution for 3 minutes, add it to the laser particle size analyzer for measurement. The particle size of Ca(OH)2 after refinement is usually D50 = 3 μm - 6 μm, D97 = 12 μm - 25 μm. After grinding and dispersion, reaching the predetermined values means D50 ≤ 2 μm, D97 ≤ 10 μm.

4. The preparation method of nano calcium carbonate for photovoltaic sealant according to claim 1, characterized in that, In step S3, adjust the temperature of the raw slurry to 15°C - 30°C, and adjust the concentration of the raw slurry to a mass percentage concentration, with the concentration adjusted to 5% - 12%.

5. The preparation method of nano calcium carbonate for photovoltaic sealant according to claim 1, characterized in that, In step S4, introduce kiln gas for the second time. The concentration of CO2 in the kiln gas is 25% - 40%. The particle size of the primary nano calcium carbonate slurry is D50 = 2 μm - 5 μm, D97 = 7 μm - 16 μm. Turn on the circulation emulsifier for grinding and stirring; when the detected laser particle size reaches the required particle size D50 ≤ 1.0 μm, D97 ≤ 6 μm, introduce kiln gas for the second time.

6. The preparation method of nano calcium carbonate for photovoltaic sealant according to claim 1, characterized in that, The organic polyol is one or more of dibromoneopentyl glycol, dibromobutylene glycol, bromine-containing polyether diol, bromine-containing polyester diol, and tetrabromobisphenol A bis(hydroxyethoxy) ether; the salts are one or more of zinc sulfate, zinc chloride, zinc nitrate, and zinc dihydrogen phosphate.

7. A preparation method of nano calcium carbonate for photovoltaic sealant according to any one of claims 1 to 6, characterized in that, The pH of nano calcium carbonate is 8 - 10, the moisture content is < 0.5%, the oil absorption value is 20 g DOP / 100 g - 30 g DOP / 100 g, the specific surface area is 30 m 2 / g - 45 m 2 / g, the laser particle size means D50 ≤ 1.0 μm, D97 ≤ 10.0 μm, the blue light whiteness ≥ 95%, the hue L value ≥ 94.5, the a value ≤ 0, the b value ≤ 3.2, the blue light whiteness after aging ≥ 93.5%, the hue L value after aging ≥ 93%, the a value ≤ 1, the b value ≤ 4.

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