Wet ground calcium carbonate for improving elongation at break of polyvinyl chloride and preparation method of wet ground calcium carbonate

Abstract

The invention provides wet ground calcium carbonate for improving the elongation at break of polyvinyl chloride and a preparation method of the wet ground calcium carbonate, and belongs to the technical field of functional inorganic non-metallic materials. The preparation method comprises the following steps: mixing calcium carbonate coarse powder, a dispersing agent A and water to prepare slurry, and sequentially carrying out wet grinding, wet modification, flash drying and dry modification on the slurry to obtain the wet heavy calcium carbonate for improving the elongation at break of polyvinyl chloride. According to the invention, a composite modification process is adopted, and a liquid modifier is added in a boiled slurry stirring process for wet modification; the dried powder is subjected to dry modification, so that the surface modification effect of calcium carbonate is improved, and the interfacial compatibility with a PVC base material is improved.

Description

Technical Field

[0001] This invention relates to the field of functional inorganic non-metallic materials technology, and in particular to a wet-process heavy calcium carbonate and its preparation method for improving the elongation at break of polyvinyl chloride. Background Technology

[0002] Polyvinyl chloride (PVC) is a polymer formed by the polymerization of vinyl chloride monomers through a free polymerization mechanism under the action of initiators such as peroxides and azo compounds, or under the influence of light and heat. PVC is the world's most produced general-purpose plastic with a wide range of applications. It is widely used in building materials, industrial products, daily necessities, flooring, artificial leather, pipes, wires and cables, films, and sealing materials.

[0003] Heavy calcium carbonate, due to its low price, is a commonly used filler in PVC production as it can reduce costs when added to PVC. Wet-process heavy calcium carbonate, with its fine particle size and narrow distribution, can improve the hardness, rigidity, and dimensional stability of PVC when added, while also enhancing its processing fluidity during production.

[0004] As market demands and customer needs for cost reduction increase, the amount of calcium carbonate added to PVC products is also rising. However, with increased calcium carbonate content, the strength and elongation of PVC decrease. This is because excessive calcium carbonate occupies the space between PVC molecular chains, restricting their movement and increasing internal defects and inhomogeneities, leading to a decline in mechanical properties, particularly elongation at break.

[0005] Given the high-speed and rapid production requirements of downstream PVC manufacturers, and the need to maintain good elongation at break after adding calcium carbonate, developing a wet-process heavy calcium carbonate that improves the elongation at break of PVC is a technical problem that needs to be solved through process optimization and upgrading. Summary of the Invention

[0006] The purpose of this invention is to provide a wet-process heavy calcium carbonate and its preparation method for improving the elongation at break of polyvinyl chloride, so as to solve the above-mentioned technical problems.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] This invention provides a method for preparing wet-process heavy calcium carbonate to improve the elongation at break of polyvinyl chloride, comprising the following steps:

[0009] Calcium carbonate coarse powder, dispersant A and water are mixed to form a slurry. The slurry is then subjected to wet grinding, wet modification, flash drying and dry modification in sequence to obtain wet heavy calcium carbonate that improves the elongation at break of polyvinyl chloride.

[0010] Dispersant B is added during the wet grinding process, modifier C is added during the wet modification process, and modifier D is added during the dry modification process.

[0011] Furthermore, the mass ratio of the crude calcium carbonate powder to water is 60-75:25-40, and the mass ratio of the dispersant A to the crude calcium carbonate powder is 1-8:1000.

[0012] Furthermore, the dispersant A is a medium-to-low molecular weight sodium polyacrylate with a weight-average molecular weight of 2000-5000.

[0013] The dispersant B comprises one or more of sodium hexametaphosphate, sodium oleate, sodium dodecyl sulfate, sodium benzenesulfonate, polycarboxylate, polyacrylate, and potassium lauryl ether phosphate.

[0014] Furthermore, the wet grinding is a vertical wet grinding process, with the slurry fed from the bottom and discharged from the top, the grinding speed being 2000-3500 r / min, and the grinding time being 20-60 min;

[0015] During the wet grinding process, an aqueous solution of dispersant B is added. The mass ratio of dispersant B to water is 6-15:1000, and the amount of aqueous solution of dispersant B added is 50-150 L / h.

[0016] Furthermore, the wet modification temperature is 70–90°C, and the wet modification time is 20–60 min; the amount of modifier C added is 2–10‰ of the slurry mass, and modifier C contains one or more of polyethylene glycol, polyvinyl alcohol, polymaleic acid, sodium stearate, sodium methyl stearate polyoxyethylene ether sulfonate, isooctanol phosphate, and isooctanol ether phosphate.

[0017] Furthermore, the inlet air temperature of the flash dryer is 300-360℃, the outlet air temperature is 100-150℃, and the dryer blade speed is 1000-2000 r / min.

[0018] Furthermore, the dry modification is carried out using a high-speed mixer, with a modification time of 10–30 min and a modification temperature of 100–130 °C.

[0019] Furthermore, the amount of modifier D added is 2 to 10‰ of the mass of the calcium carbonate powder, and modifier D contains one or more of stearic acid, glyceryl monooleate, glyceryl monostearate, glyceryl monostearate, trimellitate, pentaerythritol oleate, and distearate phthalate.

[0020] The present invention also provides wet-process heavy calcium carbonate prepared by the above preparation method to improve the elongation at break of polyvinyl chloride.

[0021] The beneficial effects of this invention are:

[0022] (1) The ultrafine calcium carbonate prepared by the present invention using a wet grinding process has a D50 of 1.8–2.2 μm and a specific surface area ≥10 m². 2 Compared with traditional ultrafine calcium carbonate processing techniques, the calcium carbonate particles prepared by this invention have a finer particle size and a larger specific surface area, thus avoiding the reduction in PVC toughness caused by large particle size. Large particle size increases stress concentration points within the material, disrupting the continuity of the PVC molecular chain; however, the ultrafine calcium carbonate prepared using this invention, due to its fine particle size, avoids the problems caused by large particles when added to the PVC molecular chain.

[0023] (2) This invention employs a wet grinding process, adding different dispersants during slurry preparation and wet grinding to ensure good dispersibility of the ultrafine calcium carbonate particles. Due to the fine particle size, if the particles are not well dispersed in the PVC system, they can easily agglomerate, forming larger agglomerates. These agglomerates are equivalent to defects in the PVC substrate, and when subjected to external forces, stress tends to concentrate at these defects, making the material more prone to fracture and other damage. This invention improves the dispersibility between calcium carbonate particles by adding different types of dispersants.

[0024] (3) This invention employs a composite modification process to improve the compatibility between calcium carbonate and PVC substrate. Due to the poor compatibility between calcium carbonate and PVC, the interfacial bonding force between them is weak. When PVC is subjected to external force, debonding easily occurs at the interface, preventing calcium carbonate from effectively cooperating with the PVC matrix to withstand the external force, thereby reducing the overall mechanical properties. This invention employs a composite modification process, adding a liquid modifier during the stirring of the slurry for wet modification; the dried powder undergoes dry modification, improving the surface modification effect of calcium carbonate and enhancing its interfacial compatibility with the PVC substrate. Detailed Implementation

[0025] This invention provides a method for preparing wet-process heavy calcium carbonate to improve the elongation at break of polyvinyl chloride, comprising the following steps:

[0026] Calcium carbonate coarse powder, dispersant A and water are mixed to form a slurry. The slurry is then subjected to wet grinding, wet modification, flash drying and dry modification in sequence to obtain wet heavy calcium carbonate that improves the elongation at break of polyvinyl chloride.

[0027] Dispersant B is added during the wet grinding process, modifier C is added during the wet modification process, and modifier D is added during the dry modification process.

[0028] In this invention, the mass ratio of the crude calcium carbonate powder to water is 60-75:25-40, preferably 65-70:30-35, and more preferably 70:30; the mass ratio of the dispersant A to the crude calcium carbonate powder is 1-8:1000, preferably 2-5:1000, and more preferably 3:1000.

[0029] In this invention, the dispersant A is a medium-to-low molecular weight sodium polyacrylate with a weight-average molecular weight of 2000-5000, preferably 2000-3000.

[0030] The dispersant B comprises one or more of sodium hexametaphosphate, sodium oleate, sodium dodecyl sulfate, sodium benzenesulfonate, polycarboxylate, polyacrylate, and potassium lauryl ether phosphate, preferably one or more of sodium hexametaphosphate, sodium oleate, sodium dodecyl sulfate, sodium benzenesulfonate, and polycarboxylate.

[0031] In this invention, the wet grinding is a vertical wet grinding process, the slurry is fed from the bottom and discharged from the top, the grinding speed is 2000-3500 r / min, preferably 3000 r / min; the grinding time is 20-60 min, preferably 30-50 min, and more preferably 40 min;

[0032] The wet grinding process involves adding an aqueous solution of dispersant B, wherein the mass ratio of dispersant B to water is 6–15:1000, preferably 8–12:1000, and more preferably 10–12:1000; the amount of aqueous solution of dispersant B added is 50–150 L / h, preferably 80–120 L / h, and more preferably 90 L / h.

[0033] In this invention, the temperature of the wet modification is 70-90°C, preferably 80°C; the time of the wet modification is 20-60 min, preferably 30-50 min, and more preferably 40 min; the amount of modifier C added is 2-10‰ of the slurry mass, preferably 4-8‰, and more preferably 6‰; the modifier C contains one or more of polyethylene glycol, polyvinyl alcohol, polymaleic acid, sodium stearate, sodium methyl stearate polyoxyethylene ether sulfonate, isooctanol phosphate, and isooctanol ether phosphate, preferably one or more of polyethylene glycol, polyvinyl alcohol, polymaleic acid, and sodium stearate.

[0034] In this invention, the inlet air temperature of the flash dryer is 300-360°C, preferably 330°C; the outlet air temperature is 100-150°C, preferably 110°C; and the dryer blade rotation speed is 1000-2000 r / min, preferably 1200-1800 r / min, and more preferably 1500 r / min.

[0035] In this invention, the dry modification is carried out using a high-speed mixer, the modification time is 10-30 min, preferably 20 min, and the modification temperature is 100-130℃, preferably 120℃.

[0036] In this invention, the amount of modifier D added is 2-10‰ of the mass of calcium carbonate powder, preferably 4-8‰, and more preferably 6‰; modifier D contains one or more of stearic acid, glyceryl monooleate, glyceryl monostearate, glyceryl monostearate, trimellitate, pentaerythritol oleate, and distearate, preferably one or more of stearic acid, glyceryl monooleate, glyceryl monostearate, glyceryl monostearate, and trimellitate.

[0037] The present invention also provides wet-process heavy calcium carbonate prepared by the above preparation method to improve the elongation at break of polyvinyl chloride.

[0038] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0039] Example 1

[0040] 650 kg of coarse calcium carbonate powder (D97: 30.18 μm), 350 kg of water, and 2.6 kg of sodium polyacrylate were weighed and transferred to a slurry tank to prepare a slurry. After stirring for 10-15 minutes, the slurry was pumped to a vertical wet mill for wet grinding. During the wet grinding process, an aqueous dispersant solution containing sodium hexametaphosphate was added using a flow pump at a rate of 90 L / h. The mass ratio of sodium hexametaphosphate to water in the aqueous solution was 12:1000. The grinding speed was 3000 r / min, and the grinding time was 45 minutes. The ground slurry was then filtered through a 250-mesh sieve and transferred to a slurry preparation tank for wet modification. During the modification process, 4 kg of sodium methyl stearate polyoxyethylene ether sulfonate was added, the modification temperature was 80℃, and the modification time was 45 min. The wet-modified slurry was flash-dried at a blade speed of 1440 r / min, an inlet air temperature of 340℃, and an outlet air temperature of 135℃. The dried powder was then conveyed to a high-speed mixer for dry modification, in which 1.3 kg of stearic acid and 1.5 kg of glyceryl monostearate were added, the modification time was 15 min, and the modification temperature was 110℃. After cooling, the modified powder was packaged using an automatic packaging machine to obtain wet-process heavy calcium carbonate with improved elongation at break of polyvinyl chloride.

[0041] Example 2

[0042] Weigh 600 kg of coarse calcium carbonate powder (D97: 30.18 μm), 400 kg of water, and 1.8 kg of sodium polyacrylate into a slurry tank to prepare a slurry. After stirring for 10-15 min, the slurry is pumped to a vertical wet mill for wet grinding. During the wet grinding process, an aqueous dispersant solution containing sodium dodecyl sulfate and polyacrylate is added using a flow pump at a rate of 90 L / h. The mass ratio of sodium dodecyl sulfate and polyacrylate to water in the aqueous solution is 12:1000. The grinding speed is 3000 r / min, and the grinding time is 45 min. After grinding, the slurry is filtered through a 250-mesh sieve and then transferred to a slurry preparation tank for wet grinding. The product undergoes a wet modification process, with 3 kg of polyethylene glycol and 3 kg of isooctanol phosphate added during the wet modification. The modification temperature is 80℃, and the modification time is 45 min. The wet-modified slurry is then flash-dried at a blade speed of 1440 r / min, an inlet air temperature of 330℃, and an outlet air temperature of 130℃. The dried powder is then conveyed to a high-speed mixer for dry modification, where 1.2 kg of stearic acid and 1.2 kg of distearate phthalate are added during the dry modification. The modification time is 15 min, and the modification temperature is 110℃. After cooling, the modified powder is packaged using an automatic packaging machine to obtain wet-process heavy calcium carbonate with improved elongation at break of polyvinyl chloride.

[0043] Example 3

[0044] 700 kg of coarse calcium carbonate powder (D97: 30.18 μm), 300 kg of water, and 2.1 kg of sodium polyacrylate were weighed and transferred to a slurry tank to prepare a slurry. After stirring for 10-15 min, the slurry was pumped to a vertical wet mill for wet grinding. During the wet grinding process, an aqueous dispersant solution containing sodium oleate and polycarboxylate was added using a flow pump at a rate of 90 L / h. The mass ratio of sodium oleate and polycarboxylate to water in the aqueous solution was 12:1000. The grinding speed was 3000 r / min, and the grinding time was 45 min. The ground slurry was then filtered through a 250-mesh sieve and transferred to a slurry preparation tank for wet modification. In the wet modification process, 3 kg of sodium stearate and 4 kg of isooctanol phosphate were added, the modification temperature was 80℃, and the modification time was 45 min. The slurry after wet modification was flash dried at a blade speed of 1440 r / min, an inlet air temperature of 330℃, and an outlet air temperature of 130℃. The dried powder was then conveyed to a high-speed mixer for dry modification, in which 1.2 kg of monooleate glycerol and 1.8 kg of pentaerythritol oleate were added, the modification time was 15 min, and the modification temperature was 110℃. After cooling, the modified powder was packaged using an automatic packaging machine to obtain wet-process heavy calcium carbonate with improved elongation at break of polyvinyl chloride.

[0045] Example 4

[0046] 750 kg of coarse calcium carbonate powder (D97: 30.18 μm), 250 kg of water, and 2.3 kg of sodium polyacrylate were weighed and transferred to a slurry tank to prepare a slurry. After stirring for 10-15 min, the slurry was pumped to a vertical wet mill for wet grinding. During the wet grinding process, an aqueous dispersant solution containing sodium benzenesulfonate and polycarboxylate was added using a flow pump at a rate of 90 L / h. The mass ratio of sodium benzenesulfonate and polycarboxylate to water in the aqueous solution was 12:1000. The grinding speed was 3000 r / min, and the grinding time was 45 min. After grinding, the slurry was filtered through a 250-mesh sieve and then transferred to a finishing tank for wet modification. In the wet modification process, 3 kg of polyvinyl alcohol and 4 kg of isooctanol phosphate were added, the modification temperature was 80℃, and the modification time was 45 min. The wet-modified slurry was flash-dried at a blade speed of 1440 r / min, an inlet air temperature of 330℃, and an outlet air temperature of 130℃. The dried powder was then conveyed to a high-speed mixer for dry modification, in which 1.5 kg of glyceryl monostearate and 1.5 kg of pentaerythritol oleate were added, the modification time was 15 min, and the modification temperature was 110℃. After cooling, the modified powder was packaged using an automatic packaging machine to obtain wet-process heavy calcium carbonate with improved elongation at break of polyvinyl chloride.

[0047] Example 5

[0048] 700 kg of coarse calcium carbonate powder (D97: 30.18 μm), 300 kg of water, and 2.1 kg of sodium polyacrylate were weighed and transferred to a slurry tank to prepare a slurry. After stirring for 10-15 min, the slurry was pumped to a vertical wet mill for wet grinding. During the wet grinding process, an aqueous dispersant solution containing sodium hexametaphosphate and polycarboxylate was added using a flow pump at a rate of 90 L / h. The mass ratio of sodium hexametaphosphate and polycarboxylate to water in the aqueous solution was 12:1000. The grinding speed was 3000 r / min, and the grinding time was 45 min. The ground slurry was then filtered through a 250-mesh sieve and transferred to a slurry preparation tank for wet modification. During the modification process, 3 kg of polyethylene glycol and 3 kg of sodium stearate polyoxyethylene ether sulfonate were added. The modification temperature was 80℃ and the modification time was 45 min. The wet-modified slurry was flash-dried at a blade speed of 1440 r / min, an inlet air temperature of 330℃, and an outlet air temperature of 130℃. The dried powder was then conveyed to a high-speed mixer for dry modification. During dry modification, 1.5 kg of glyceryl monostearate and 1.5 kg of trimellitate were added. The modification time was 15 min and the modification temperature was 110℃. After cooling, the modified powder was packaged using an automatic packaging machine to obtain wet-process heavy calcium carbonate with improved elongation at break of polyvinyl chloride.

[0049] Example 6

[0050] 700 kg of coarse calcium carbonate powder (D97: 30.18 μm), 300 kg of water, and 2.1 kg of sodium polyacrylate were weighed and transferred to a slurry tank to prepare a slurry. After stirring for 10-15 min, the slurry was pumped to a vertical wet mill for wet grinding. During the wet grinding process, an aqueous dispersant solution containing sodium dodecyl sulfate and polycarboxylate was added using a flow pump at a rate of 90 L / h. The mass ratio of sodium dodecyl sulfate and polycarboxylate to water in the aqueous solution was 12:1000. The grinding speed was 3000 r / min, and the grinding time was 45 min. After grinding, the slurry was filtered through a 250-mesh sieve and then transferred to a slurry preparation tank for wet modification. In the wet modification process, 3 kg of polyethylene glycol and 3 kg of isooctanol phosphate were added, the modification temperature was 80℃, and the modification time was 45 min. The wet-modified slurry was flash-dried at a blade speed of 1440 r / min, an inlet air temperature of 330℃, and an outlet air temperature of 130℃. The dried powder was then conveyed to a high-speed mixer for dry modification, in which 1.5 kg of glyceryl monostearate and 1.5 kg of distearate phthalate were added, the modification time was 15 min, and the modification temperature was 110℃. After cooling, the modified powder was packaged using an automatic packaging machine to obtain wet-process heavy calcium carbonate with improved elongation at break of polyvinyl chloride.

[0051] Comparative Example 1

[0052] CC-2800 calcium carbonate produced by the ring roller mill of Jiangxi Guangyuan Chemical Co., Ltd.

[0053] Comparative Example 2

[0054] GY-916 calcium carbonate produced by ball milling at Jiangxi Guangyuan Chemical Co., Ltd.

[0055] Comparative Example 3

[0056] GY-816 calcium carbonate produced by vertical mill of Lianzhou Guangyuan Calcium Carbonate Co., Ltd.

[0057] Comparative Example 4

[0058] (Single wet modification) Weigh 700 kg of coarse calcium carbonate powder (D97: 30.18 μm), 300 kg of water, and 2.1 kg of sodium polyacrylate into a slurry tank to prepare a slurry. After stirring for 10-15 min, the slurry is pumped to a vertical wet mill for wet grinding. During the wet grinding process, a dispersant aqueous solution containing sodium dodecyl sulfate and polycarboxylate is added using a flow pump at a rate of 90 L / h. The mass ratio of sodium dodecyl sulfate and polycarboxylate to water in the aqueous solution is 12:1000. The grinding speed is... The grinding speed was 3000 r / min, and the grinding time was 45 min. The ground slurry was filtered through a 250-mesh sieve and then transported to a slurry tank for wet modification. During the wet modification process, 3 kg of polyethylene glycol and 3 kg of isooctanol phosphate were added. The modification temperature was 80℃, and the modification time was 45 min. The wet-modified slurry was then flash-dried. The dryer blade speed was 1440 r / min, the inlet air temperature was 330℃, and the outlet air temperature was 130℃. The dried powder was collected, cooled, and then packaged using an automatic packaging machine to obtain wet-process heavy calcium carbonate.

[0059] Comparative Example 5

[0060] (Dry modification only) Weigh 700 kg of coarse calcium carbonate powder (D97: 30.18 μm), 300 kg of water, and 2.1 kg of sodium polyacrylate into a slurry tank to prepare a slurry. After stirring for 10-15 min, pump the slurry into a vertical wet mill for wet grinding. During the wet grinding process, add an aqueous dispersant solution containing sodium hexametaphosphate and polycarboxylate using a flow pump. The addition rate of the aqueous solution is 90 L / h, and the mass ratio of sodium hexametaphosphate and polycarboxylate to water in the aqueous solution is 12:1000. The grinding speed is 3000 r / min. The grinding time was 45 minutes. The ground slurry was filtered through a 250-mesh sieve and then transported to a slurry tank for stirring. The stirred slurry was then flash-dried at a blade speed of 1440 r / min, an inlet air temperature of 330℃, and an outlet air temperature of 130℃. The dried powder was then transported to a high-speed mixer for dry modification. 1.5 kg of glyceryl monostearate and 1.5 kg of trimellitate were added during the dry modification process. The modification time was 15 minutes and the modification temperature was 110℃. After cooling, the modified powder was packaged using an automatic packaging machine to obtain wet-process heavy calcium carbonate.

[0061] Comparative Example 6

[0062] (Without modification) Weigh 700 kg of coarse calcium carbonate powder (D97: 30.18 μm), 300 kg of water, and 2.1 kg of sodium polyacrylate into a slurry tank to prepare a slurry. After stirring for 10-15 min, the slurry is pumped to a vertical wet grinding mill for wet grinding. During the wet grinding process, a dispersant aqueous solution containing sodium hexametaphosphate and polycarboxylate is added using a flow pump at a rate of 90 L / h. The mass ratio of sodium hexametaphosphate and polycarboxylate to water in the aqueous solution is 12:1000. The grinding speed is 3000 r / min, and the grinding time is 45 min. The ground slurry is filtered through a 250-mesh sieve and then transferred to a slurry tank for stirring. The stirred slurry is then flash-dried at a blade speed of 1440 r / min, an inlet air temperature of 330℃, and an outlet air temperature of 130℃. The dried powder is collected, cooled, and then packaged using an automatic packaging machine to obtain wet-process heavy calcium carbonate.

[0063] Performance testing

[0064] Performance tests were performed on the products from Examples 1-6 and Comparative Examples 1-6:

[0065] 1. Particle size distribution test: The particle size distribution was tested using a BT-9300ST laser particle size analyzer from Liaoning Dandong Better Co., Ltd., where D50 represents the particle size value corresponding to a cumulative distribution of 50%; D97 represents the particle size value corresponding to a cumulative distribution of 97%.

[0066] 2. Oil absorption value test:

[0067] The oil absorption value test is specifically conducted as follows:

[0068] Weigh 5g of the product (accurate to 0.01g) and place it on a glass plate. While mixing the product with a spatula, add dioctyl phthalate (DOP) dropwise, stirring continuously until the added DOP completely binds the product together, i.e., until saturation is reached. Record the volume of DOP consumed.

[0069] Oil absorption value = v / m × 100

[0070] m: Weight of the product (in grams);

[0071] v: Volume of DOP consumed (in mL);

[0072] The unit for oil absorption value is mL / 100g.

[0073] 3. Specific surface area test:

[0074] The tests were conducted using a CANTA NOVA2000e fully automated specific surface area and pore size distribution analyzer via liquid nitrogen adsorption.

[0075] Table 1: Performance test results of Examples 1-6 and Comparative Examples 1-6

[0076]

[0077] As can be seen from the results in Table 1, the ultrafine calcium carbonate prepared using this invention has a D50 of 1.8-2.2 μm, an oil absorption value of 20-22 mL / 100 g, and a specific surface area ≥11 m². 2 / g. Compared with the traditional dry production process (Comparative Examples 1-3), it significantly increases the specific surface area of ​​calcium carbonate powder. The larger the specific surface area, the more particles there are for the same weight, and the finer the powder. When applied to PVC, it has a stronger stress-bearing capacity and better performance.

[0078] The composite modification process of this invention aims to reduce the problem of high oil absorption value of ultrafine calcium carbonate prepared by wet process. Using a wet process without modification (Comparative Example 6), the oil absorption value of the powder is 35 mL / 100g. The oil absorption value of calcium carbonate prepared by a single wet modification process (Comparative Example 4) is 26 mL / 100g, and the oil absorption value of calcium carbonate prepared by a single dry modification process (Comparative Example 5) is 28 mL / 100g. The oil absorption value of ultrafine calcium carbonate prepared by this invention is 20-22 mL / 100g. Compared with the unmodified process, the oil absorption value of calcium carbonate prepared by this invention is reduced by 37%-42%; compared with a single wet modification process, the oil absorption value is reduced by 15%-23%; and compared with a single dry modification process, the oil absorption value is reduced by 21%-28%. When applied to PVC, the lower the oil absorption value of calcium carbonate, the less lubricant and plasticizer are needed. In other words, with the same amount of lubricant and plasticizer added, calcium carbonate powder with a lower oil absorption value can be more compatible with PVC substrate and improve its mechanical properties.

[0079] The test results from the examples show that the calcium carbonate prepared by the present invention achieves a continuous integrated production process of dispersion and modification. Compared with the traditional modification process, it has strong continuous production stability, and the process flow is basically a closed operation, which improves production efficiency and promotes the protection of the production environment and the physical and mental health of the operators.

[0080] Application effect evaluation:

[0081] To verify the application effect of the ultrafine calcium carbonate prepared by the present invention in PVC, the raw materials of Examples 1-6 and Comparative Examples 1-6 were weighed according to the formula and prepared, and applied to the PVC system to test its effect.

[0082] Experimental materials: PVC: SG-5 type, Cangzhou Julong Chemical Co., Ltd.; DOTP: AVIC New Materials (Shandong) Co., Ltd.; Liquid barium cadmium zinc composite stabilizer: Wenzhou Zhengbang Chemical Co., Ltd.; Calcium carbonate: Examples 1-6 and Comparative Examples 1-6; Titanium dioxide: R902, Chemours Chemical (Shanghai) Co., Ltd.

[0083] Experimental Procedure: Accurately weigh each raw material according to the following ratio: PVC: 200g; DOTP: 80g; stabilizer: 8g; titanium dioxide: 10g; calcium carbonate: 110g. Mix thoroughly and then refine on a two-roll mill for no more than 10 minutes at a temperature of 170℃. Next, press the mixture into 3-4mm thick samples in a flat vulcanizing press at 170℃ for 3 minutes, followed by a cooling time of approximately 30 seconds. Finally, cut the samples into strips that meet the testing requirements for testing.

[0084] Tensile strength and elongation at break tests: conducted in accordance with GB / T1040.1-2018.

[0085] Table 2: Test results of tensile strength and elongation at break of the prepared PVC strips

[0086] Group Tensile strength (MPa) Elongation at break (%) Example 1 15.95 161.7 Example 2 15.92 162.3 Example 3 15.96 161.3 Example 4 15.98 162.6 Example 5 15.96 163.7 Example 6 15.94 162.5 Comparative Example 1 15.07 131.5 Comparative Example 2 15.32 135.6 Comparative Example 3 15.03 134.3 Comparative Example 4 15.33 150.2 Comparative Example 5 15.32 145.1 Comparative Example 6 15.11 140.2

[0087] Analysis of the test results of the PVC strips prepared in Table 2 shows that the tensile strength of the strips in Examples 1-6 is improved to varying degrees compared with that in Comparative Examples 1-6, although the improvement is not very significant. The elongation at break is significantly improved; the elongation at break of the PVC strips prepared in Examples 1-6 is all above 161%. The results of Examples 3 (161.3%), with the lowest elongation at break, and Example 5 (163.7%), with the highest elongation at break, are compared with those of Comparative Examples 1-6 for further analysis. The elongation at break of Example 3 was 18.47% higher than that of Comparative Example 1, and the elongation at break of Example 5 was 19.67% higher than that of Comparative Example 1; the elongation at break of Example 3 was 15.93% higher than that of Comparative Example 2, and the elongation at break of Example 5 was 17.16% higher than that of Comparative Example 2; the elongation at break of Example 3 was 16.73% higher than that of Comparative Example 3, and the elongation at break of Example 5 was 17.95% higher than that of Comparative Example 3; the elongation at break of Example 3 was 6.88% higher than that of Comparative Example 4, and the elongation at break of Example 5 was 8.24% higher than that of Comparative Example 4; the elongation at break of Example 3 was 10.04% higher than that of Comparative Example 5, and the elongation at break of Example 5 was 11.36% higher than that of Comparative Example 6; the elongation at break of Example 3 was 13.08% higher than that of Comparative Example 6, and the elongation at break of Example 5 was 14.35% higher than that of Comparative Example 6.

[0088] Based on the data analysis results of Examples 1-6 applied to PVC, the wet-process ultrafine calcium carbonate prepared by the present invention has a significant effect on improving the elongation at break when applied to PVC.

[0089] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing wet-process heavy calcium carbonate to improve the elongation at break of polyvinyl chloride, characterized in that, Includes the following steps: Calcium carbonate coarse powder, dispersant A and water are mixed to form a slurry. The slurry is then subjected to wet grinding, wet modification, flash drying and dry modification in sequence to obtain wet heavy calcium carbonate that improves the elongation at break of polyvinyl chloride. Dispersant B is added during the wet grinding process, modifier C is added during the wet modification process, and modifier D is added during the dry modification process.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the crude calcium carbonate powder to water is 60-75:25-40, and the mass ratio of the dispersant A to the crude calcium carbonate powder is 1-8:1000.

3. The preparation method according to claim 1 or 2, characterized in that, The dispersant A is sodium polyacrylate with a medium to low molecular weight and a weight-average molecular weight of 2000 to 5000. The dispersant B comprises one or more of sodium hexametaphosphate, sodium oleate, sodium dodecyl sulfate, sodium benzenesulfonate, polycarboxylate, polyacrylate, and potassium lauryl ether phosphate.

4. The preparation method according to claim 3, characterized in that, The wet grinding is a vertical wet grinding process, with the slurry fed from the bottom and discharged from the top. The grinding speed is 2000-3500 r / min and the grinding time is 20-60 min. During the wet grinding process, an aqueous solution of dispersant B is added. The mass ratio of dispersant B to water is 6-15:1000, and the amount of aqueous solution of dispersant B added is 50-150 L / h.

5. The preparation method according to claim 1, 2, or 4, characterized in that, The wet modification temperature is 70-90℃, and the wet modification time is 20-60 min; the amount of modifier C added is 2-10‰ of the slurry mass, and modifier C contains one or more of polyethylene glycol, polyvinyl alcohol, polymaleic acid, sodium stearate, sodium methyl stearate polyoxyethylene ether sulfonate, isooctanol phosphate, and isooctanol ether phosphate.

6. The preparation method according to claim 5, characterized in that, The flash dryer has an inlet air temperature of 300–360°C, an outlet air temperature of 100–150°C, and a blade rotation speed of 1000–2000 r / min.

7. The preparation method according to claim 1 or 6, characterized in that, The dry modification process employs a high-speed mixer for 10–30 min and a temperature of 100–130 °C.

8. The preparation method according to claim 7, characterized in that, The amount of modifier D added is 2 to 10‰ of the mass of the calcium carbonate powder. Modifier D contains one or more of stearic acid, glyceryl monooleate, glyceryl monostearate, glyceryl monostearate, trimellitate, pentaerythritol oleate, and distearate phthalate.

9. Wet-process heavy calcium carbonate with improved elongation at break of polyvinyl chloride prepared by the preparation method according to any one of claims 1 to 8.

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