Flame-retardant high-impact calcium carbonate master batch, PVC (polyvinyl chloride) cable conduit and preparation method of PVC cable conduit

Abstract

The invention relates to the technical field of PVC cable conduits, in particular to a flame-retardant high-impact calcium carbonate master batch, a PVC cable conduit and a preparation method thereof.The preparation method of the flame-retardant high-impact calcium carbonate master batch comprises the steps that calcium carbonate, zinc borate and stearic acid are pretreated and put into a stirring machine at the same time to be mixed and modified for the first time; diluting a silane coupling agent, and adjusting the pH value to obtain a silane coupling agent solution; drying the first coated calcium carbonate to obtain second coated calcium carbonate; spraying a silane coupling agent solution on the surface of the second coating calcium carbonate by using a spraying device, carrying out second mixing modification, drying and crushing to obtain the flame-retardant high-impact calcium carbonate master batch; the calcium carbonate and the zinc borate in the flame-retardant high-impact calcium carbonate master batch have good dispersibility, so that the dispersion stability of the calcium carbonate and the zinc borate in a PVC matrix is improved, and the problem that the impact resistance and the flame retardance of the PVC cable conduit cannot be further improved due to poor dispersibility of the calcium carbonate and the zinc borate in the existing flame-retardant calcium carbonate is solved.

Description

Technical Field

[0001] This invention relates to the field of PVC cable conduit technology, and particularly to flame-retardant, high-impact calcium carbonate masterbatch, PVC cable conduits, and their preparation methods. Background Technology

[0002] PVC cable conduits are widely used in power, telecommunications, and other fields. Their core function is to provide mechanical, chemical, and environmental protection for cables. Impact resistance and flame retardancy are two key indicators ensuring their safe application. Currently, a suitable amount of calcium carbonate is commonly added during the production of PVC cable conduits to improve impact resistance. However, calcium carbonate has strong hydrophilic hydroxyl groups on its surface. This hydrophilic property makes calcium carbonate incompatible with the PVC matrix, resulting in uneven dispersion of calcium carbonate within the PVC product and failing to further improve its impact resistance. Regarding flame retardancy, non-halogenated flame retardants are gradually replacing traditional halogenated flame retardants in the market. Non-halogenated flame retardants do not produce carcinogens during the reaction process, making them more environmentally friendly and healthier. Zinc borate, as a non-halogenated flame retardant, has advantages such as being halogen-free, environmentally friendly, low-corrosion, and having excellent smoke suppression effects, and it is also widely added to PVC cable conduits.

[0003] However, both calcium carbonate and zinc borate are inorganic materials, which are prone to agglomeration and poor dispersibility during actual processing. Therefore, to leverage the impact resistance of calcium carbonate and the flame retardant properties of zinc borate, manufacturers often use modifiers to surface-modify calcium carbonate and zinc borate. Surface modification is divided into dry modification and wet modification. Dry modification involves using mechanical shearing, mixing, or other external forces in a dry state to uniformly adhere the modifier (such as stearic acid or silane coupling agents) to the powder surface. Wet modification uses water or organic solvents as the dispersion medium to disperse the powder into a suspension, then adds the modifier, and finally filters, dries, and pulverizes to obtain the modified powder.

[0004] Flame-retardant calcium carbonate products that can simultaneously improve the impact resistance and flame retardancy of PVC cable conduits have appeared on the market. These flame-retardant calcium carbonate products are then blended and extruded with a PVC matrix to produce PVC cable conduits. The preparation method for flame-retardant calcium carbonate products generally involves first modifying calcium carbonate with a modifier, then modifying zinc borate with a modifier, and finally mixing the modified calcium carbonate and zinc borate to obtain the flame-retardant calcium carbonate product. However, the dispersion of calcium carbonate and zinc borate in the resulting flame-retardant high-impact calcium carbonate masterbatch is poor, failing to fully utilize the impact resistance of calcium carbonate and the flame-retardant properties of zinc borate. When the flame-retardant calcium carbonate product is added to the PVC matrix, the calcium carbonate and zinc borate are unevenly distributed within the PVC product, thus failing to further improve the impact resistance and flame retardancy of the PVC cable conduit. Summary of the Invention

[0005] To address the problems raised in the background art, the present invention aims to provide a method for preparing flame-retardant high-impact calcium carbonate masterbatch. The prepared flame-retardant high-impact calcium carbonate masterbatch exhibits good dispersibility of both calcium carbonate and zinc borate, which is beneficial for improving the dispersion stability of calcium carbonate and zinc borate in the PVC matrix. This further enhances the impact resistance and flame retardancy of PVC cable conduits. This method solves the problem that existing flame-retardant calcium carbonate products have poor dispersibility of calcium carbonate and zinc borate, failing to fully utilize the impact resistance of calcium carbonate and the flame retardant effect of zinc borate. Furthermore, when flame-retardant calcium carbonate products are added to PVC cable conduits, the uneven distribution of calcium carbonate and zinc borate within the product prevents further improvement in the impact resistance and flame retardancy of the PVC cable conduits.

[0006] Another objective of this invention is to propose a flame-retardant high-impact calcium carbonate masterbatch prepared by the above-described preparation method. Both calcium carbonate and zinc borate in the flame-retardant high-impact calcium carbonate masterbatch have good dispersibility, which is beneficial to improving the dispersion stability of calcium carbonate and zinc borate in the PVC matrix, and can further improve the impact resistance and flame retardancy of PVC cable conduits.

[0007] Another objective of this invention is to provide a PVC cable conduit comprising the flame-retardant and high-impact calcium carbonate masterbatch prepared by the above-described preparation method. The calcium carbonate and zinc borate exhibit high dispersion stability in the PVC matrix, and this PVC cable conduit possesses the advantages of high impact resistance and high flame retardancy.

[0008] Another objective of this invention is to propose the above-mentioned method for preparing PVC cable conduits, which achieves efficient blending of various raw materials, high dispersion stability of calcium carbonate and zinc borate in the PVC matrix, and the resulting PVC cable conduits have the advantages of high impact resistance and high flame retardancy.

[0009] To achieve the above objectives, this invention proposes a method for preparing flame-retardant, high-impact calcium carbonate masterbatch, comprising the following steps: Step S1: First, calcium carbonate, zinc borate and stearic acid are pretreated. Then, the calcium carbonate, zinc borate and stearic acid are simultaneously put into a stirring machine for the first mixing and modification to obtain the first coated calcium carbonate. Step S2: Dilute the silane coupling agent with anhydrous ethanol, adjust the pH to obtain a silane coupling agent solution; dry the first coated calcium carbonate to obtain the second coated calcium carbonate. Step S3: Use a spraying device to spray the silane coupling agent solution onto the surface of the second coated calcium carbonate, perform a second mixing modification, and obtain flame-retardant and high-impact calcium carbonate masterbatch after drying and pulverizing.

[0010] Optionally, in step S1, the pretreatment includes drying the calcium carbonate and zinc borate to control the moisture content of the calcium carbonate and zinc borate to below 0.5%. The pretreatment also includes grinding the stearic acid to control the particle size of the stearic acid to 80-100 mesh.

[0011] Optionally, in step S1, the temperature of the first mixing modification is 80-100℃, the time is 15-30 min, and the rotation speed of the stirring machine is 1500-2000 rpm.

[0012] Optionally, in step S2, the volume ratio of the silane coupling agent to the anhydrous ethanol is 1:1; acetic acid is used to adjust the pH, and the pH of the silane coupling agent solution is 4-5; the water content of the second coated calcium carbonate is ≤0.5%.

[0013] Optionally, the silane coupling agent is selected from KH-550.

[0014] Optionally, in step S3, the spraying speed of the spraying device is 0.5-1.2 m / s, the atomization pressure is 0.2-0.5 MPa, and the droplet size after atomization by the spraying device is 20-80 μm.

[0015] Optionally, in step S3, the flame-retardant, high-impact calcium carbonate masterbatch has a moisture content of ≤0.5% and a particle size of 80-100 mesh.

[0016] The present invention also proposes a flame-retardant and high-impact calcium carbonate masterbatch, which is prepared using any of the above-described methods for preparing flame-retardant and high-impact calcium carbonate masterbatch. The flame-retardant and high-impact calcium carbonate masterbatch comprises the following raw materials in parts by weight: 100 parts of calcium carbonate, 4-6 parts of zinc borate, 1.5-2.5 parts of stearic acid, and 4-8 parts of silane coupling agent.

[0017] The present invention also proposes a PVC cable conduit, wherein the PVC cable conduit comprises the following raw materials in parts by weight: The flame-retardant and high-impact calcium carbonate masterbatch prepared by any of the above methods consists of 28-34 parts of flame-retardant and high-impact calcium carbonate masterbatch, 100 parts of PVC matrix, 4-5 parts of calcium-zinc stabilizer, 1 part of polyethylene wax, 9 parts of chlorinated polyethylene and 2 parts of titanium dioxide.

[0018] The present invention also proposes a method for preparing PVC cable conduits, which is used to prepare the above-mentioned PVC cable conduits. The preparation method includes: thoroughly mixing the flame-retardant high-impact calcium carbonate masterbatch, the PVC matrix, the calcium-zinc stabilizer, the polyethylene wax, the chlorinated polyethylene and the titanium dioxide, and then co-extruding the mixture using a twin-screw extruder to obtain the PVC cable conduit.

[0019] Compared with the prior art, the embodiments of the present invention have the following beneficial effects: 1. This invention employs a two-stage simultaneous surface modification treatment for calcium carbonate and zinc borate. Stearic acid, as a primary modifier, reacts first with calcium carbonate and zinc borate, while a silane coupling agent, as a secondary modifier, reacts with them. The invention first uses stearic acid for the initial mixing modification, leveraging its high coverage to uniformly coat the surfaces of calcium carbonate and zinc borate. At this stage, zinc borate and stearic acid jointly coat the calcium carbonate, forming the first coated calcium carbonate. Stearic acid effectively reduces the agglomeration of calcium carbonate and zinc borate, improving their dispersibility and ensuring uniform distribution within the PVC matrix. Next, a silane coupling agent is used. This agent strengthens interfacial bonding, effectively enhancing the interfacial bond between calcium carbonate, zinc borate, and stearic acid. This prevents weak interfacial bonds from being easily broken by mechanical shear forces. The second coating is achieved by using a silane coupling agent. Coating calcium carbonate with zinc borate, stearic acid, and silane coupling agent avoids the limitation of silane coupling agent coverage, which could affect the modification effect. The resulting flame-retardant high-impact calcium carbonate masterbatch exhibits good dispersibility of calcium carbonate and zinc borate. The synergistic effect of stearic acid and silane coupling agent further improves the dispersion stability of calcium carbonate and zinc borate in the PVC matrix. This invention further enhances the impact resistance and flame retardancy of PVC cable conduits. It also avoids the problem of poor dispersion of calcium carbonate and zinc borate leading to easy deposition of flame-retardant calcium carbonate products in molds and screws. This solves the problem of poor dispersion of calcium carbonate and zinc borate in existing flame-retardant calcium carbonate products, which fails to fully utilize the impact resistance of calcium carbonate and the flame retardancy of zinc borate. Furthermore, when flame-retardant calcium carbonate products are added to PVC cable conduits, the uneven distribution of calcium carbonate and zinc borate within the product prevents further improvement in the impact resistance and flame retardancy of the PVC cable conduits.

[0020] 2. Both modification processes used in this invention are dry modifications. The first mixing modification is carried out using a stirring machine, and the second mixing modification is carried out using a spraying device to spray a silane coupling agent solution onto the dry second-coated calcium carbonate surface. This invention uses few types of solvents, only anhydrous ethanol. Therefore, this invention does not require steps such as filtration, drying, and waste solvent treatment, which simplifies the preparation method. Moreover, anhydrous ethanol can evaporate quickly with the airflow during the preparation process, avoiding residual impurities and ensuring the compatibility between the subsequent flame-retardant and high-impact calcium carbonate masterbatch and the PVC matrix. Furthermore, stearic acid modification requires high-temperature conditions, while silane coupling agents are prone to hydrolysis and inactivation at high temperatures. Silane coupling agent modification requires relatively low-temperature conditions. If stearic acid and silane coupling agents are added simultaneously, the modification temperature cannot be balanced, resulting in poor modification effects for both. Moreover, stearic acid will preemptively occupy the active sites on the calcium carbonate surface, thus hindering the grafting of the silane coupling agent and reducing its modification efficiency. Therefore, this invention adopts a stepwise addition method for stearic acid and silane coupling agents, eliminating the need to balance the modification temperature, simplifying the preparation method, and ensuring that the silane coupling agent has a high modification efficiency. This is beneficial for improving the dispersion stability of calcium carbonate and zinc borate in the PVC matrix, thereby further improving the impact resistance and flame retardancy of PVC cable conduits.

[0021] 3. The present invention employs a spray device, which enables the silane coupling agent solution to uniformly cover the second coated calcium carbonate, preventing the silane coupling agent from agglomerating, effectively enhancing the interfacial bonding force between calcium carbonate, zinc borate and stearic acid, and further ensuring the interfacial bonding force between calcium carbonate, zinc borate and PVC matrix. Detailed Implementation

[0022] This invention proposes a method for preparing flame-retardant and high-impact calcium carbonate masterbatch, comprising the following steps: Step S1: First, calcium carbonate, zinc borate and stearic acid are pretreated. Then, calcium carbonate, zinc borate and stearic acid are simultaneously put into a stirring machine for the first mixing and modification to obtain the first coated calcium carbonate. Step S2: Dilute the silane coupling agent with anhydrous ethanol, adjust the pH to obtain a silane coupling agent solution; dry the first coated calcium carbonate to obtain the second coated calcium carbonate. Step S3: Use a spraying device to spray the silane coupling agent solution onto the surface of the second coated calcium carbonate, perform a second mixing modification, and obtain flame-retardant and high-impact calcium carbonate masterbatch after drying and pulverizing.

[0023] This invention employs a two-stage simultaneous surface modification treatment for calcium carbonate and zinc borate. Stearic acid, as the primary modifier, reacts first with both calcium carbonate and zinc borate, while a silane coupling agent, as the secondary modifier, reacts with them again. The invention first uses stearic acid for a first-stage mixing modification, leveraging its high coverage to uniformly coat the surfaces of calcium carbonate and zinc borate. At this stage, zinc borate and stearic acid jointly coat the calcium carbonate, forming the first layer of coated calcium carbonate. Stearic acid effectively reduces the agglomeration of calcium carbonate and zinc borate, improving their dispersibility and ensuring uniform distribution within the PVC matrix. Next, a silane coupling agent is used. This agent strengthens interfacial bonding, effectively enhancing the interfacial bond between calcium carbonate, zinc borate, and stearic acid. This prevents the weak interfacial bond from being easily damaged by mechanical shear forces. The second layer of coated calcium carbonate is then formed using the silane coupling agent. In this process, calcium carbonate is coated with zinc borate, stearic acid, and a silane coupling agent. This avoids the limitation of the silane coupling agent's coverage, which could affect the modification effect. The resulting flame-retardant high-impact calcium carbonate masterbatch exhibits good dispersibility of calcium carbonate and zinc borate. The synergistic effect of stearic acid and the silane coupling agent further improves the dispersion stability of calcium carbonate and zinc borate in the PVC matrix. The flame-retardant high-impact calcium carbonate masterbatch prepared by this invention can further improve the impact resistance and flame retardancy of PVC cable conduits. It also avoids the problem of poor dispersion of calcium carbonate and zinc borate, which can lead to the deposition of flame-retardant calcium carbonate products in molds and screws. This invention solves the problem that existing flame-retardant calcium carbonate products have poor dispersibility of calcium carbonate and zinc borate, which cannot fully utilize the impact resistance of calcium carbonate and the flame retardancy of zinc borate. When flame-retardant calcium carbonate products are added to PVC cable conduits, the uneven distribution of calcium carbonate and zinc borate within the product prevents further improvement in the impact resistance and flame retardancy of PVC cable conduits.

[0024] Furthermore, both modification processes employed in this invention are dry modifications. The first mixing modification is performed using a stirring machine, while the second mixing modification is performed using a spraying device to spray a silane coupling agent solution onto the dry surface of the second coated calcium carbonate. This invention uses fewer types of solvents, employing only anhydrous ethanol. Therefore, this invention eliminates the need for steps such as filtration, drying, and waste solvent disposal, simplifying the preparation method. Moreover, anhydrous ethanol can evaporate rapidly with the airflow during the preparation process, avoiding residual impurities and ensuring the compatibility between the subsequent flame-retardant and high-impact calcium carbonate masterbatch and the PVC matrix. Furthermore, stearic acid modification requires high-temperature conditions, while silane coupling agents are prone to hydrolysis and inactivation at high temperatures. Silane coupling agent modification requires relatively low-temperature conditions. If stearic acid and silane coupling agents are added simultaneously, the modification temperature cannot be balanced, resulting in poor modification effects for both. Moreover, stearic acid will preemptively occupy the active sites on the calcium carbonate surface, thus hindering the grafting of the silane coupling agent and reducing its modification efficiency. Therefore, this invention adopts a stepwise addition method for stearic acid and silane coupling agents, eliminating the need to balance the modification temperature, simplifying the preparation method, and ensuring that the silane coupling agent has a high modification efficiency. This is beneficial for improving the dispersion stability of calcium carbonate and zinc borate in the PVC matrix, thereby further improving the impact resistance and flame retardancy of PVC cable conduits.

[0025] Furthermore, the present invention employs a spraying device, which enables the silane coupling agent solution to uniformly cover the second coated calcium carbonate, preventing the silane coupling agent from agglomerating and effectively enhancing the interfacial bonding force between calcium carbonate, zinc borate, and stearic acid, thereby further ensuring the interfacial bonding force between calcium carbonate, zinc borate, and the PVC matrix.

[0026] To further explain, the coverage of silane coupling agents is limited, specifically because the coverage of silane coupling agents is easily limited by the specific surface area of ​​the powders (i.e., calcium carbonate and zinc borate). If the specific surface area of ​​calcium carbonate and zinc borate is large (particle size is inversely proportional to specific surface area; the larger the particle size, the smaller the specific surface area), then the coverage of the silane coupling agent will be low, and the modification effect will be poor.

[0027] To further explain, during the first mixing modification in this invention, the calcium ions (Ca) on the surface of calcium carbonate... 2+ Zinc ions (Zn) on the surface of zinc borate 2+Zinc borate and stearic acid combine with the carboxyl groups (-COOH) of stearic acid to form stable chemical bonds. Zinc borate and stearic acid together coat calcium carbonate, forming the first layer of coated calcium carbonate. At this point, a hydrophobic layer forms on the surface of both calcium carbonate and zinc borate, effectively reducing agglomeration and improving their dispersibility. The prepared flame-retardant, high-impact calcium carbonate masterbatch exhibits high dispersibility of calcium carbonate and zinc borate. The formation of the hydrophobic layer enhances compatibility with the PVC matrix, further improving the impact resistance and flame retardancy of PVC cable conduits. Furthermore, the carboxyl groups (-COOH) of stearic acid and the zinc ions (Zn) of zinc borate... 2+ The reaction produces zinc stearate (Zn(C)). 17 H 35 This metallic soap (COO)2 can bridge the zinc borate and PVC matrix, providing a stable interfacial bond and further improving the flame retardancy of PVC cable conduits. Furthermore, the zinc borate decomposes at high temperatures to generate a flame-retardant layer (B2O3), and stearic acid undergoes a carbonization reaction at high temperatures to generate carbonization products. The synergistic effect of the flame-retardant layer and the carbonization products together blocks oxygen and heat transfer, resulting in a synergistic flame-retardant effect.

[0028] In the second mixing modification stage of this invention, the alkoxy group (-OR) of the silane coupling agent undergoes a hydrolysis reaction to generate silanol (-SiOH). The silanol (-SiOH) reacts with the hydroxyl groups on the surface of calcium carbonate to form Si-O-Ca covalent bonds. The silanol (-SiOH) also reacts with the hydroxyl groups on the surface of zinc borate to form Si-O-Zn covalent bonds. At this point, based on the second coating of calcium carbonate, a second coating of calcium carbonate is applied using the silane coupling agent. Thus, zinc borate, stearic acid, and the silane coupling agent jointly coat calcium carbonate. The silane coupling agent enhances the interfacial bonding between calcium carbonate, zinc borate, and stearic acid, and also strengthens the interfacial bonding between calcium carbonate, zinc borate, and the PVC matrix, thereby enhancing the inorganic-organic interfacial bonding. In subsequent production, the organic functional groups (such as amino and epoxy groups) of the silane coupling agent react with the PVC matrix to form a cross-linked network. At this point, calcium carbonate and zinc borate are tightly connected to the PVC matrix through the silane coupling agent, thereby improving the product's impact resistance and flame retardancy. In addition, when exposed to high temperatures or combustion environments, zinc borate decomposes to generate a flame-retardant layer B2O3, and silanol condenses with hydroxyl groups to form covalent bonds. Under the combined effect of the flame-retardant layer B2O3 and covalent bonds, the impact resistance and flame retardancy of PVC cable conduits are further improved.

[0029] Furthermore, zinc borate possesses environmentally friendly properties, meeting the restrictions on the generation of toxic substances. At temperatures above 320°C, zinc borate undergoes dehydration and decomposition, releasing water of crystallization for physical cooling. Simultaneously, it generates a glassy B₂O₃ flame-retardant layer to block oxygen and heat transfer, and also catalyzes and inhibits free radical chain reactions during combustion. Therefore, zinc borate exhibits multiple flame-retardant and smoke-suppressing mechanisms. Compared to aluminum hydroxide, zinc borate has higher thermal stability, making it more suitable for high-temperature processing. Compared to magnesium hydroxide, zinc borate has the advantage of requiring a lower dosage, while magnesium hydroxide requires a high addition amount to achieve the desired flame-retardant effect. Therefore, after comprehensive consideration, the applicant ultimately chose zinc borate as a non-halogenated flame retardant.

[0030] In one embodiment of the present invention, in step S1, the pretreatment includes drying calcium carbonate and zinc borate to control the water content of calcium carbonate and zinc borate to below 0.5% (meaning that the percentage of their water mass to the sample mass is less than 0.5%). Pretreatment also includes grinding stearic acid to control the particle size of stearic acid to 80-100 mesh.

[0031] The high-temperature dehydration and charring ability of zinc borate is closely related to its crystal water content. If the crystal water content is too high, zinc borate will release water prematurely before reaching the ideal flame-retardant temperature, reducing its flame-retardant effect and thus affecting the flame retardancy of PVC cable conduits. To avoid this, the water content of zinc borate should be controlled below 0.5%. If the water content of calcium carbonate is too high, calcium carbonate will undergo hydrolysis during the subsequent processing of the PVC matrix, causing fluctuations in the viscosity of the PVC melt. This increases the difficulty of mixing and extruding the flame-retardant, high-impact calcium carbonate masterbatch with the PVC matrix using a twin-screw extruder, failing to effectively improve the impact resistance and flame retardancy of PVC cable conduits. In addition, if the particle size of stearic acid is too large, its specific surface area will be small. As a result, the dispersibility of stearic acid is low during the first mixing modification. Stearic acid cannot fully and uniformly coat calcium carbonate and zinc borate, which affects the dispersibility of calcium carbonate and zinc borate and cannot further improve the impact resistance and flame retardancy of PVC cable conduits. Therefore, by controlling the particle size of stearic acid, the modification effect of stearic acid on calcium carbonate and zinc borate can be fully utilized.

[0032] Preferably, calcium carbonate and zinc borate are dried at 100°C.

[0033] Preferably, stearic acid is ground using a pulverizer.

[0034] In one embodiment of the present invention, in step S1, the temperature of the first mixing modification is 80-100℃, the time is 15-30 min, and the speed of the stirring machine is 1500-2000 rpm.

[0035] By controlling the temperature and time of the first mixing modification, the reaction efficiency between calcium carbonate, zinc borate, and stearic acid was accelerated, enabling stearic acid to react with calcium ions (CaO) on the surface of calcium carbonate. 2+ ), hydroxyl groups and zinc ions (Zn) on the surface of zinc borate 2+ To ensure a complete reaction, stearic acid is uniformly coated on calcium carbonate and zinc borate, thus fully modifying the calcium carbonate and zinc borate. By controlling the rotation speed of the stirring machine, a good mixing effect is achieved between calcium carbonate, zinc borate, and stearic acid, thereby ensuring that calcium carbonate and zinc borate can fully react with stearic acid.

[0036] Preferably, the mixing machinery is a honeycomb mill.

[0037] In one embodiment of the present invention, in step S2, the volume ratio of silane coupling agent to anhydrous ethanol is 1:1; acetic acid is used to adjust the pH, and the pH of the silane coupling agent solution is 4-5; the water content of the second coated calcium carbonate is ≤0.5% (meaning that the percentage of its water mass to the sample mass is less than 0.5%).

[0038] By setting the volume ratio of silane coupling agent to anhydrous ethanol to 1:1, the silane coupling agent is ensured to be fully dissolved and uniformly dispersed in the anhydrous ethanol. This also avoids the situation where the volume of the silane coupling agent is too large, resulting in high liquid viscosity, further ensuring that the silane coupling agent fully modifies calcium carbonate and zinc borate. This invention uses acetic acid to adjust the pH. Acetic acid provides a weakly acidic environment, which increases the hydrolysis rate of the silane coupling agent, further ensuring that the silane coupling agent hydrolyzes to generate sufficient silanols. It also avoids unnecessary damage to the structure of the silane coupling agent caused by the use of strong acids or bases. By controlling the water content of the second coated calcium carbonate to 0.5% or less, the aggregation of the silane coupling agent due to excessive water content in the second coated calcium carbonate is avoided. This further ensures that the silane coupling agent is uniformly attached to the surface of calcium carbonate and zinc borate, thereby improving the interfacial bonding force between calcium carbonate, zinc borate, and stearic acid.

[0039] Preferably, the first coated calcium carbonate is dried at 100°C.

[0040] In one embodiment of the present invention, the silane coupling agent is selected from KH-550.

[0041] The silane coupling agent is selected from KH-550 (γ-aminopropyltriethoxysilane), which improves the interfacial bonding force between calcium carbonate, zinc borate and stearic acid, and can further improve the interfacial bonding force between calcium carbonate, zinc borate and PVC matrix. Moreover, the silane coupling agent has high modification efficiency and low cost, which can reduce the production cost of this invention.

[0042] In one embodiment of the present invention, in step S3, the spraying speed of the spraying device is 0.5-1.2 m / s, the atomization pressure is 0.2-0.5 MPa, and the droplet size after atomization by the spraying device is 20-80 μm.

[0043] The spraying device is used to spray the silane coupling agent solution onto the second-coated calcium carbonate. If the spraying speed is too fast, some droplets will bounce due to excessive kinetic energy, failing to adhere effectively and uniformly to the second-coated calcium carbonate. If the atomization pressure is too low, or the atomized droplets are too large, large droplets will form on the surface of the second-coated calcium carbonate. In this case, the silane coupling agent will aggregate on the surface of the second-coated calcium carbonate, preventing it from fully reacting with calcium carbonate and zinc borate. Therefore, by controlling the spraying speed, atomization pressure, and droplet size of the spraying device, the uniformity of the silane coupling agent's coating on the second-coated calcium carbonate can be improved, enhancing the interfacial bonding between calcium carbonate, zinc borate, and stearic acid in the flame-retardant high-impact calcium carbonate masterbatch, and further fully utilizing the impact resistance of calcium carbonate and the flame-retardant effect of zinc borate.

[0044] To further explain, the spraying device can be a rotary sprayer that can adjust the spraying speed, atomization pressure and the size of the atomized droplets. The present invention does not limit the specific type of spraying device.

[0045] In one embodiment of the present invention, in step S3, the moisture content of the flame-retardant high-impact calcium carbonate masterbatch is ≤0.5%, and the particle size is 80-100 mesh.

[0046] By controlling the moisture content of flame-retardant high-impact calcium carbonate masterbatch to below 0.5%, high compatibility between the masterbatch and PVC matrix can be ensured. By controlling the particle size of the flame-retardant high-impact calcium carbonate masterbatch to 80-100 mesh, the situation of excessively large particle size and small specific surface area can be avoided. At this size, the particle size of the flame-retardant high-impact calcium carbonate masterbatch has a suitable specific surface area, further ensuring high dispersibility of calcium carbonate and zinc borate in the masterbatch, which is beneficial to improving the dispersion stability of calcium carbonate and zinc borate in PVC matrix.

[0047] Preferably, the flame-retardant and high-impact calcium carbonate masterbatch is dried at 100°C, and then pulverized using a pulverizer.

[0048] The present invention also proposes a flame-retardant and high-impact calcium carbonate masterbatch, which is prepared by the above-mentioned preparation method of flame-retardant and high-impact calcium carbonate masterbatch. The flame-retardant and high-impact calcium carbonate masterbatch comprises the following raw materials in parts by weight: 100 parts of calcium carbonate, 4-6 parts of zinc borate, 1.5-2.5 parts of stearic acid and 4-8 parts of silane coupling agent.

[0049] The flame-retardant and high-impact calcium carbonate masterbatch prepared by this invention using appropriate weight parts of calcium carbonate, zinc borate, stearic acid, and silane coupling agent exhibits good dispersibility of calcium carbonate and zinc borate, which is beneficial to improving the dispersion stability of calcium carbonate and zinc borate in the PVC matrix. The flame-retardant and high-impact calcium carbonate masterbatch prepared by this invention can further improve the impact resistance and flame retardancy of PVC cable conduits, and can also avoid the situation where flame-retardant calcium carbonate products are prone to deposition in the mold due to poor dispersion of calcium carbonate and zinc borate.

[0050] The present invention also proposes a PVC cable conduit comprising the following raw material composition in parts by weight: The above-mentioned method for preparing flame-retardant and high-impact calcium carbonate masterbatch yields 28-34 parts of flame-retardant and high-impact calcium carbonate masterbatch, 100 parts of PVC matrix, 4-5 parts of calcium-zinc stabilizer, 1 part of polyethylene wax, 9 parts of chlorinated polyethylene, and 2 parts of titanium dioxide.

[0051] The present invention also proposes a PVC cable conduit comprising the above-mentioned flame-retardant and high-impact calcium carbonate masterbatch. The calcium carbonate and zinc borate in the flame-retardant and high-impact calcium carbonate masterbatch have good dispersibility, and the dispersion stability of calcium carbonate and zinc borate in the PVC matrix is ​​high. Therefore, the present PVC cable conduit has the advantages of high impact resistance and high flame retardancy.

[0052] The present invention also proposes a method for preparing PVC cable conduits, which is used to prepare the above-mentioned PVC cable conduits. The preparation method includes: thoroughly mixing flame-retardant high-impact calcium carbonate masterbatch, PVC matrix, calcium zinc stabilizer, polyethylene wax, chlorinated polyethylene and titanium dioxide, and then co-extruding the mixture using a twin-screw extruder to obtain PVC cable conduits.

[0053] This invention also proposes a method for preparing PVC cable conduits. By using a twin-screw extruder for co-extrusion, efficient blending of various raw materials can be achieved. Furthermore, calcium carbonate and zinc borate in the flame-retardant and high-impact calcium carbonate masterbatch have good dispersibility, and the dispersion stability of calcium carbonate and zinc borate in the PVC matrix is ​​high. The resulting PVC cable conduit has the advantages of high impact resistance and high flame retardancy.

[0054] Preferably, the screw speed of the twin-screw extruder is 200-300 rpm, and the temperature gradient is 160-180℃.

[0055] To facilitate understanding of the present invention, a more complete description is provided below. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0056] Where specific techniques or conditions are not specified in the examples and comparative examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products, including: The calcium carbonate was purchased from Guangxi Hongshan New Material Technology Co., Ltd., model number XL-2500. Zinc borate was purchased from Jinan Sennuo New Material Technology Co., Ltd., model number ZB. Stearic acid was purchased from Shijiazhuang Bojian Fine Chemical Co., Ltd., and its product type was 1801. The silane coupling agent was purchased from Shandong Silicon Science New Materials Co., Ltd., and its model number is KH-550.

[0057] Example 1 This embodiment provides a method for preparing flame-retardant, high-impact calcium carbonate masterbatch, including the following steps: Step S1: First, calcium carbonate, zinc borate, and stearic acid are pretreated. The pretreatment includes drying calcium carbonate and zinc borate at 100°C to control the moisture content of calcium carbonate and zinc borate at 0.5%. The pretreatment also includes grinding stearic acid using a pulverizer to control the particle size of stearic acid at 90 mesh. Then, calcium carbonate, zinc borate, and stearic acid are simultaneously placed into a mixing machine (a honeycomb mill) for the first mixing modification. The temperature of the first mixing modification is 100°C, the time is 30 minutes, and the speed of the honeycomb mill is 2000 rpm to obtain the first coated calcium carbonate. Step S2: The silane coupling agent is selected from KH-550. It is diluted with anhydrous ethanol at a volume ratio of 1:1. After adjusting the pH with acetic acid, a silane coupling agent solution is obtained with a pH of 5. The first coated calcium carbonate is dried at 100°C to obtain the second coated calcium carbonate, which has a water content of 0.5%. Step S3: Using a spraying device (a rotary sprayer), the silane coupling agent solution is sprayed onto the surface of the second coated calcium carbonate. The spraying speed of the spraying device is 1.2 m / s, the atomization pressure is 0.5 MPa, and the droplet size after atomization is 80 μm. A second mixing modification is performed. After drying (at 100°C) and pulverizing (using a pulverizer), flame-retardant high-impact calcium carbonate masterbatch is obtained. The moisture content of the flame-retardant high-impact calcium carbonate masterbatch is 0.5%, and the particle size is 100 mesh.

[0058] This flame-retardant, high-impact calcium carbonate masterbatch comprises the following raw materials in parts by weight: 100 parts calcium carbonate, 4 parts zinc borate, 1.5 parts stearic acid, and 4 parts silane coupling agent.

[0059] Example 2 The difference between Example 2 and Example 1 is that in step S1, the water content of calcium carbonate and zinc borate is controlled at 0.3%, the particle size of stearic acid is controlled at 80 mesh, the temperature of the first mixing modification is 80℃, the time is 15min, and the speed of the stirring machine (the stirring machine is a honeycomb mill) is 1500rpm.

[0060] Example 3 The difference between Example 3 and Example 1 is that in step S2, the pH of the silane coupling agent solution is 4; and the water content of the second coated calcium carbonate is 0.3%.

[0061] Example 4 The difference between Example 4 and Example 1 is that in step S3, the spraying speed of the spraying device is 0.5 m / s, the atomization pressure is 0.2 MPa, and the droplet size after atomization by the spraying device is 20 μm; the water content of the flame-retardant high-impact calcium carbonate masterbatch is 0.3%, and the particle size is 80 nm.

[0062] Examples 5-9 The difference between Examples 5-9 and Example 1 lies in the different weight percentages of the raw materials in the flame-retardant, high-impact calcium carbonate masterbatch. The specific weight percentages of the raw materials for the flame-retardant, high-impact calcium carbonate masterbatch in Examples 5-9 are shown in Table 1.

[0063] Table 1. Raw material weight parts (unit: parts) for flame-retardant and high-impact calcium carbonate masterbatches in Examples 5-9 Comparative Example 1 By weight, take 20 parts calcium carbonate, 4.5 parts zinc borate, 1.5 parts stearic acid, 4.5 parts silane coupling agent, 100 parts PVC matrix, 5 parts calcium zinc stabilizer, 1 part polyethylene wax, 9 parts chlorinated polyethylene (CPE) and 2 parts titanium dioxide, mix thoroughly, and then use a twin-screw extruder to co-extrude and prepare PVC cable conduits.

[0064] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that calcium carbonate, zinc borate, stearic acid and silane coupling agent are simultaneously placed into a mixing machine (a honeycomb mill) for mixing and modification. After drying (at 100°C) and pulverizing (using a pulverizer), flame-retardant and high-impact calcium carbonate masterbatch is obtained.

[0065] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that in step S1, the water content of calcium carbonate is controlled to be 2%.

[0066] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that in step S1, the water content of zinc borate is controlled to be 2%.

[0067] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that, in step S1, the particle size of stearic acid is controlled at 60-70 mesh.

[0068] Comparative Example 6 The difference between Comparative Example 6 and Example 1 is that in step S2, the water content of the second coated calcium carbonate is controlled to be 2%.

[0069] Performance testing The flame-retardant and high-impact calcium carbonate masterbatches prepared in Examples 1-9 and Comparative Examples 2-6 were used to prepare PVC cable conduits according to Table 2. Then, the PVC cable conduits of Examples 1-9 and Comparative Examples 1-6 were tested for impact performance according to GB / T43815-2024 "Rigid Polyvinyl Chloride (PVC-U) Insulating Electrical Conduits and Fittings for Building", oxygen index according to GB / T2406.2-2009 and self-extinguishing property according to GB / T2408-2021. The test results are shown in Tables 3, 4 and 5.

[0070] Table 2 Raw material composition of PVC cable conduits (by weight parts) Table 3 Performance test results of Examples 1 to 4 Table 4 Performance test results of Examples 5 to 9 Table 5 Performance test results for Comparative Examples 1 to 6 As can be seen from Tables 3 and 4, Examples 1-9 exhibit higher impact resistance, higher oxygen index, and shorter self-extinguishing time. This invention employs simultaneous two-stage surface modification treatments for calcium carbonate and zinc borate. First, stearic acid is used for the initial mixing modification, leveraging its high coverage to ensure uniform coverage of the calcium carbonate and zinc borate surfaces. Then, a silane coupling agent is used, which enhances interfacial bonding, effectively strengthening the interfacial bond between calcium carbonate, zinc borate, and stearic acid. The resulting flame-retardant, high-impact calcium carbonate masterbatch exhibits good dispersibility of calcium carbonate and zinc borate, improving their dispersion stability in the PVC matrix. The flame-retardant, high-impact calcium carbonate masterbatch prepared by this invention can further improve the impact resistance and flame retardancy of PVC cable conduits.

[0071] As can be seen from Table 5, the PVC cable conduits in Comparative Examples 1-6 have poor impact resistance and flame retardancy.

[0072] Comparative Example 1 did not use stearic acid and silane coupling agent to modify calcium carbonate and zinc borate simultaneously. Instead, it directly mixed calcium carbonate, zinc borate, stearic acid, and silane coupling agent with the PVC matrix. As a result, the modification effect of stearic acid and silane coupling agent on calcium carbonate and zinc borate was poor. At this time, the calcium carbonate and zinc borate were unevenly distributed inside the PVC cable conduit, resulting in poor impact resistance and flame retardancy of Comparative Example 1.

[0073] In Comparative Example 2, calcium carbonate, zinc borate, stearic acid, and silane coupling agent were simultaneously mixed and modified in a honeycomb mill. During the modification process, stearic acid preemptively occupied the surface active sites of calcium carbonate and zinc borate, reducing the number of surface active sites and hindering the grafting of the silane coupling agent. This resulted in low modification efficiency of the silane coupling agent, which could not fully modify calcium carbonate and zinc borate. The interfacial bonding force between stearic acid, calcium carbonate, and zinc borate in the flame-retardant and high-impact calcium carbonate masterbatch was weak, which could not improve the dispersibility of calcium carbonate and zinc borate. Calcium carbonate and zinc borate were unevenly distributed inside the PVC cable conduit. Therefore, Comparative Example 2 had poor impact resistance and flame retardancy.

[0074] In Comparative Example 3, the moisture content of calcium carbonate was controlled at 2%. The high moisture content of calcium carbonate caused hydrolysis during the subsequent processing of the PVC matrix, resulting in fluctuations in the viscosity of the PVC melt. This increased the difficulty of mixing and extruding the flame-retardant and high-impact calcium carbonate masterbatch with the PVC matrix using a twin-screw extruder. Consequently, it failed to effectively improve the impact resistance and flame retardancy of the PVC cable conduit. Therefore, Comparative Example 3 had poor impact performance, low oxygen index, and long self-extinguishing time.

[0075] In Comparative Example 4, the moisture content of zinc borate was controlled at 2%. The high moisture content of zinc borate would cause it to release moisture before reaching the ideal flame retardant temperature, resulting in a reduction in the flame retardant effect of zinc borate and thus affecting the flame retardancy of PVC cable conduits. Therefore, Comparative Example 4 had a low oxygen index and a long self-extinguishing time, indicating poor flame retardancy.

[0076] In Comparative Example 5, the particle size of stearic acid was controlled at 60-70 mesh. The particle size of stearic acid was relatively large, resulting in a small specific surface area. When the first mixing modification was carried out, the dispersibility of stearic acid was low, and stearic acid could not fully and uniformly coat calcium carbonate and zinc borate, thus affecting the dispersibility of calcium carbonate and zinc borate. Therefore, Comparative Example 5 had poor impact performance, low oxygen index, and long self-extinguishing time, and its impact resistance and flame retardancy were poor.

[0077] In Comparative Example 6, the moisture content of the second coated calcium carbonate was controlled at 2%. The high moisture content of the second coated calcium carbonate caused the silane coupling agent to agglomerate. The silane coupling agent could not be uniformly attached to the surface of calcium carbonate and zinc borate. Therefore, Comparative Example 6 had poor impact performance, low oxygen index, and long self-extinguishing time. In other words, Comparative Example 6 had poor impact resistance and flame retardancy.

[0078] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. Process for the preparation of flame-retardant, high-impact calcium carbonate masterbatches, characterized in that, The preparation method comprises the following steps: Step S1, pretreat the calcium carbonate, zinc borate and stearic acid, then put the calcium carbonate, zinc borate and stearic acid into a stirring machine for the first mixing modification, to obtain the first coated calcium carbonate; Step S2, dilute the silane coupling agent with anhydrous ethanol, and obtain the silane coupling agent solution after adjusting the pH value; Dry the first coated calcium carbonate to obtain the second coated calcium carbonate; Step S3, use a spraying device to spray the silane coupling agent solution on the surface of the second coated calcium carbonate, and perform the second mixing modification, then dry and crush to obtain the flame-retardant high-impact calcium carbonate master batch.

2. A process for the preparation of flame retardant high impact calcium carbonate masterbatch as claimed in claim 1, wherein, In the step S1, the pretreatment comprises drying the calcium carbonate and the zinc borate, and controlling the water content of the calcium carbonate and the zinc borate to be less than 0.5%; The pretreatment further comprises grinding the stearic acid, and controlling the particle size of the stearic acid to be 80-100 mesh.

3. A process for the preparation of flame retardant high impact calcium carbonate masterbatch as claimed in claim 2, wherein, In the step S1, the temperature of the first mixing modification is 80-100℃, the time is 15-30 min, and the rotating speed of the stirring machine is 1500-2000 rpm.

4. A process for the preparation of flame retardant high impact calcium carbonate masterbatch as claimed in claim 1, wherein, In the step S2, the volume ratio of the silane coupling agent to the anhydrous ethanol is 1:1; acetic acid is used to adjust the pH value, the pH value of the silane coupling agent solution is 4-5, and the water content of the second coated calcium carbonate is ≤0.5%.

5. The process for the preparation of flame retardant high impact calcium carbonate masterbatch as claimed in claim 4, wherein, The silane coupling agent is selected from KH-550.

6. A process for the preparation of flame retardant high impact calcium carbonate masterbatch as claimed in claim 1, wherein, In the step S3, the spraying speed of the spraying device is 0.5-1.2 m / s, the atomization pressure is 0.2-0.5 MPa, and the size of the liquid droplets after atomization of the spraying device is 20-80 μm.

7. The process for the preparation of flame retardant high impact calcium carbonate masterbatch as claimed in claim 6, wherein, In the step S3, the water content of the flame-retardant high-impact calcium carbonate master batch is ≤0.5%, and the particle size is 80-100 mesh.

8. A flame-retardant, high-impact calcium carbonate masterbatch, characterized in that, The flame-retardant high-impact calcium carbonate master batch is prepared by the preparation method of the flame-retardant high-impact calcium carbonate master batch according to any one of claims 1 to 7, and comprises the following raw material components by weight fraction: 100 parts of the calcium carbonate, 4-6 parts of the zinc borate, 1.5-2.5 parts of the stearic acid, and 4-8 parts of the silane coupling agent.

9. A PVC cable conduit, characterized in that The PVC cable conduit comprises the following raw material components by weight fraction: The flame-retardant high-impact calcium carbonate master batch is prepared by the preparation method of the flame-retardant high-impact calcium carbonate master batch according to any one of claims 1 to 7, and comprises the following raw material components by weight fraction: 100 parts of the calcium carbonate, 4-6 parts of the zinc borate, 1.5-2.5 parts of the stearic acid, and 4-8 parts of the silane coupling agent.

10. Process for the production of PVC cable conduits, characterized in that The preparation method for preparing the PVC cable conduit according to claim 9 comprises the following steps: thoroughly stirring and mixing the flame-retardant high-impact calcium carbonate master batch, the PVC matrix, the calcium-zinc stabilizer, the polyethylene wax, the chlorinated polyethylene, and the titanium white, and then blending and extruding by using a double-screw extruder to obtain the PVC cable conduit.

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