A magnesium hydroxide with self-lubricating function, and a preparation method and application thereof

Abstract

This invention relates to the field of modified magnesium hydroxide flame retardant preparation and application technology, specifically to a self-lubricating magnesium hydroxide, its preparation method, and its application. The preparation method involves: preparing an aqueous solution of magnesium salt, adding a composite crystallization guide agent, and mixing thoroughly; the composite crystallization guide agent includes an organophosphonate dispersant, a polyether polyol, and a low-molecular-weight alkyl sulfonate; adjusting the pH to weakly alkaline by adding an alkaline precipitant, conducting a precipitation reaction, and then performing a gradient-heating hydrothermal crystallization treatment; the product of the hydrothermal crystallization treatment is subjected to solid-liquid separation, washing, and drying to obtain a magnesium hydroxide matrix; the magnesium hydroxide matrix is ​​then modified with a silane coupling agent using a dry method to obtain magnesium hydroxide with self-lubricating function. The obtained magnesium hydroxide product has a low interparticle friction coefficient and possesses intrinsic self-lubricating effect. When applied to cable materials, it can significantly reduce extrusion pressure and increase wire exit speed, while maintaining excellent mechanical properties, flame retardant properties, and electrical insulation properties.

Description

Technical Field

[0001] This invention relates to a self-lubricating magnesium hydroxide, its preparation method, and its application, belonging to the technical field of modified magnesium hydroxide flame retardant preparation and application. Background Technology

[0002] Low-smoke halogen-free flame-retardant cable material uses polyolefin resin as the matrix and is filled with a large amount of magnesium hydroxide inorganic flame retardant. It has excellent properties such as halogen-free, low smoke, non-toxic, non-corrosive to equipment, flame retardant and smoke-suppressing properties, and is widely used in high-end cable fields such as rail transit, nuclear power, high-rise buildings, and new energy vehicles.

[0003] Currently, hexagonal flake magnesium hydroxide is commonly used in the industry, but it still has significant technical drawbacks in high-filler systems: conventional hexagonal flake magnesium hydroxide has sharp edges and large internal friction between particles, resulting in high processing torque, high extrusion pressure, and low wire exit speed; to improve processing fluidity, the industry often adds external lubricants such as stearic acid and EBS, but such lubricants will seriously interfere with the silane self-crosslinking system, adsorb tin catalysts, consume free radicals, resulting in a decrease in crosslinking degree and substandard gelation rate, while also reducing the mechanical properties and electrical insulation properties of the material.

[0004] In existing technologies, single silane modification can only improve interfacial compatibility and cannot reduce interparticle friction from the root cause of morphology; single morphology control is difficult to achieve both regular hexagonal columnar structure and rounded corners at the same time; traditional crystal guides are mostly single dispersants or surfactants, which cannot achieve the synergistic effect of directional growth, corner passivation and uniform dispersion, and cannot meet the comprehensive requirements of high-end silane self-crosslinking low-smoke halogen-free cable materials for high processing fluidity, high crosslinking stability and high mechanical properties.

[0005] Therefore, developing a magnesium hydroxide product that can achieve self-lubrication without the need for external lubricants, does not interfere with cross-linking, and has excellent processing performance has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] This invention addresses the shortcomings of existing technologies by providing a self-lubricating magnesium hydroxide, its preparation method, and its application. Hexagonal columnar rounded-corner magnesium hydroxide can be synthesized in a controlled manner using a composite crystal guide agent. Combined with silane chemical bonding modification, it achieves the technical effects of self-lubrication and drag reduction under high filling conditions, without interfering with silane self-crosslinking, and stable overall performance.

[0007] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for preparing magnesium hydroxide with self-lubricating function, wherein the preparation method is as follows: S1. Prepare an aqueous solution of magnesium salt, add a composite crystal form guiding agent, and mix thoroughly; the composite crystal form guiding agent includes organophosphonate dispersant, polyether polyol, and low molecular weight alkyl sulfonate; S2. Add alkaline precipitant to adjust pH to weakly alkaline, carry out precipitation reaction, and obtain magnesium hydroxide precursor slurry; S3. The precursor slurry is subjected to gradient heating hydrothermal crystallization treatment. S4. The product of hydrothermal crystallization treatment is separated into solid and liquid phases, washed, and dried to obtain a magnesium hydroxide matrix. The magnesium hydroxide matrix is ​​then modified with a silane coupling agent using a dry method to obtain magnesium hydroxide with self-lubricating function.

[0008] Further, by weight, the composite crystal form guide includes 30-50 parts of organophosphonate dispersant, 20-40 parts of polyether polyol, and 10-30 parts of low molecular weight alkyl sulfonate.

[0009] Preferably, the mass ratio of organophosphonate dispersant to polyether polyol is (1.2-1.5):1; The mass ratio of polyether polyol to low molecular weight alkyl sulfonate is (1.2-2.5):1.

[0010] Furthermore, the amount of the composite crystal guide agent added is 0.5%-3.0% of the theoretical mass of the magnesium hydroxide matrix.

[0011] Further, in step S2, an alkaline precipitant is added dropwise to adjust the pH to 9.5-11.0, and a precipitation reaction is carried out at 20-60℃ to obtain magnesium hydroxide precursor slurry.

[0012] Furthermore, in step S3, the gradient heating hydrothermal crystallization treatment includes the following processes in sequence: (1) Nucleation control angle stage: heat up to 100-120℃, corresponding to a saturated vapor pressure of 0.1-0.3 MPa, control the stirring speed at 20-40 rpm, and keep warm for 1-2 hours; (2) Uniform growth stage: Heat to 125-150℃, corresponding to a saturated vapor pressure of 0.35-0.8 MPa, and simultaneously increase the stirring speed to 40-60 rpm, and keep warm for 1-2 h; (3) Crystallization and densification stage: Heat to 155-180℃, corresponding to a saturated vapor pressure of 0.85-1.2 MPa, and simultaneously increase the stirring speed to 60-80 rpm, and keep warm for 2-3 h.

[0013] Furthermore, the silane coupling agent is at least one of vinyltrimethoxysilane and vinyltriethoxysilane; The amount of the silane coupling agent added is 0.8%-2.5% of the mass of the magnesium hydroxide matrix.

[0014] The present invention also discloses a magnesium hydroxide with self-lubricating function, wherein the magnesium hydroxide with self-lubricating function is prepared by the preparation method described in the present invention; The self-lubricating magnesium hydroxide has a hexagonal prism shape with a sheet diameter of 0.5-5 μm, a thickness-to-diameter ratio of 0.1-0.3, and smooth rounded corners without sharp edges.

[0015] The present invention also discloses an application of magnesium hydroxide with self-lubricating function, wherein the magnesium hydroxide with self-lubricating function is used as a flame-retardant filler in cable material.

[0016] Furthermore, when the magnesium hydroxide is applied to silane self-crosslinking low-smoke halogen-free cable material, it can achieve interparticle self-lubrication, reduce extrusion pressure and processing torque, and does not interfere with the crosslinking reaction or reduce the degree of crosslinking.

[0017] The beneficial effects of this invention are: The method for preparing self-lubricating magnesium hydroxide according to this invention achieves innovative morphology of magnesium hydroxide by rationally using a composite crystal form guide and coordinating with suitable hydrothermal crystallization conditions, thus realizing the intrinsic self-lubricating property of magnesium hydroxide while ensuring excellent flame retardant properties when used in cable materials. More specifically, in the preparation method of this invention, through precise control of the composite crystal form guide and the hydrothermal crystallization conditions, a special hexagonal columnar morphology with rounded corners is obtained, reducing interparticle friction from the structural source and achieving self-lubrication without the need for external lubricants. Under the same formulation, the extrusion pressure is reduced by 25-35%, and the wire exit speed is increased by 20-40%.

[0018] The self-lubricating magnesium hydroxide of this invention is modified by silane chemical bonding. The system does not contain interfering components such as stearic acid and EBS, does not adsorb tin catalysts, does not quench free radicals, has a stable gel rate, and is not affected by crosslinking efficiency, thus completely solving the industry pain point that processing and crosslinking cannot be taken into account in the prior art.

[0019] The self-lubricating magnesium hydroxide described in this invention exhibits superior dispersibility and interfacial bonding in cable materials. The rounded corner morphology of the self-lubricating magnesium hydroxide reduces stress concentration, and the silane molecular bridges enhance the compatibility between the magnesium hydroxide filler and the cable material matrix. Under high filling conditions, the tensile strength, elongation at break, oxygen index, and electrical insulation properties of the cable material are all superior to those of conventional hexagonal flake magnesium hydroxide.

[0020] The method for preparing magnesium hydroxide with self-lubricating function described in this invention adopts a conventional precipitation + hydrothermal crystallization + dry modification process, which has strong equipment versatility, mild conditions, controllable cost, and is easy to scale up for production. Attached Figure Description

[0021] Figure 1 SEM image of magnesium hydroxide with self-lubricating function prepared in Example 1; Figure 2 The image shows the SEM morphology of magnesium hydroxide prepared in Comparative Example 1. Detailed Implementation

[0022] The specific embodiments of the present invention will be described in detail below. The present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used is for describing particular embodiments only and is not intended to limit the invention.

[0024] A method for preparing magnesium hydroxide with self-lubricating function, wherein the preparation method is as follows: S1. Prepare an aqueous solution of magnesium salt, add a composite crystal form guiding agent, and mix thoroughly; the composite crystal form guiding agent includes organophosphonate dispersant, polyether polyol, and low molecular weight alkyl sulfonate; S2. Add alkaline precipitant to adjust pH to weakly alkaline, carry out precipitation reaction, and obtain magnesium hydroxide precursor slurry; S3. The precursor slurry is subjected to gradient heating hydrothermal crystallization treatment. S4. The product of hydrothermal crystallization treatment is separated into solid and liquid phases, washed, and dried to obtain a magnesium hydroxide matrix. The magnesium hydroxide matrix is ​​then modified with a silane coupling agent using a dry method to obtain magnesium hydroxide with self-lubricating function.

[0025] More specifically, the magnesium salt used in the embodiments of the present invention is magnesium chloride or magnesium sulfate, and the concentration of magnesium ions in the prepared aqueous solution is 1.0-1.2 mol / L.

[0026] More specifically, in the embodiments of the present invention, the alkaline precipitant is an aqueous solution of sodium hydroxide or ammonia.

[0027] More specifically, the washing process uses warm water (35-45℃).

[0028] Specifically, by weight, the composite crystal form guide includes 30-50 parts of organophosphonate dispersant, 20-40 parts of polyether polyol, and 10-30 parts of low molecular weight alkyl sulfonate.

[0029] Preferably, the mass ratio of organophosphonate dispersant to polyether polyol is (1.2-1.5):1; The mass ratio of polyether polyol to low molecular weight alkyl sulfonate is (1.2-2.5):1.

[0030] More specifically, the organophosphonate dispersant is selected from at least PAPEMP, HEDP, and ATMP; PAPEMP is preferred, as it plays a strong chelating and dispersing role during hydrothermal crystallization, effectively inhibiting crystal nucleus aggregation and regulating the growth direction of magnesium hydroxide crystals.

[0031] More specifically, the polyether polyol is selected from at least one of PEG-2000, PEG-4000, PEG-6000, PPG-2000, and polyether polyol 330; preferably PEG-4000 or PEG-6000, which achieves uniform growth and rounded corners of magnesium hydroxide crystals through steric hindrance effect and crystal face adsorption.

[0032] More specifically, the low molecular weight alkyl sulfonate is selected from at least one of sodium dodecyl sulfonate (SDS), sodium dodecylbenzene sulfonate (SDBS), and sodium p-toluene sulfonate; preferably SDS, which reduces the surface energy of particles through electrostatic repulsion and wetting, effectively preventing crystal nuclei from agglomerating.

[0033] In the composite crystal form guide, the organophosphonate dispersant is the core component for crystal form construction. Its phosphonate groups can be specifically and strongly adsorbed onto the (001) crystal face of magnesium hydroxide, effectively inhibiting the excessively rapid growth of crystals in the thickness direction, forcibly guiding the crystals to grow along the planar direction, forming a regular hexagonal columnar basic morphology, avoiding the occurrence of irregular agglomerated particles or irregular thick crystals, and is an essential component for realizing the hexagonal columnar structure.

[0034] Polyether polyols are essential components for achieving rounded corners. Their molecular chains have steric hindrance and selective adsorption properties, which can preferentially adsorb at the corners and vertices where crystal growth activity is highest, blunting the growth rate at the corners and transforming sharp corners into smooth rounded corner structures. This reduces the friction coefficient between particles from the root of crystal morphology and gives magnesium hydroxide particles a self-lubricating basis. Stable and controllable rounded corner effects cannot be achieved by using other dispersants or surfactants alone.

[0035] Low molecular weight alkyl sulfonates are essential components to ensure uniform crystal growth and dispersion. They can significantly reduce the interfacial tension of the reaction system, promote the synchronous generation and uniform growth of crystal nuclei, avoid particle adhesion, agglomeration and excessively wide particle size distribution, and ensure that the final magnesium hydroxide particles have uniform morphology and excellent dispersibility. This provides a guarantee for reducing extrusion pressure and improving processing fluidity under high filling conditions.

[0036] The above three components are synergistically compounded. The organophosphonate dispersant constructs a hexagonal columnar framework, the addition of polyether polyols achieves rounded corners, and low-molecular-weight alkyl sulfonates ensure uniform particle dispersion. The final product is a magnesium hydroxide with a regular morphology, smooth corners, and uniform dispersion, achieving a comprehensive technical effect of self-lubrication, low extrusion pressure, and no interference with crosslinking. Traditional morphology modifiers such as single fatty acids, silicates, phosphates, polyethylene glycol, and common surfactants only have single dispersion or weak regulation effects, failing to achieve synergistic control of hexagonal columnar morphology and rounded corners. Furthermore, residual components can interfere with the silane self-crosslinking system, leading to decreased crosslinking degree and reduced mechanical properties, thus failing to meet the requirements for low-smoke halogen-free flame-retardant cable materials.

[0037] Specifically, the amount of the composite crystal guide agent added is 0.5%-3.0% of the theoretical mass of the magnesium hydroxide matrix.

[0038] Specifically, in step S2, an alkaline precipitant is added dropwise to adjust the pH to 9.5-11.0, and a precipitation reaction is carried out at 20-60℃ to obtain magnesium hydroxide precursor slurry.

[0039] Specifically, in step S3, the gradient heating hydrothermal crystallization treatment includes the following processes in sequence: (1) Nucleation and corner control stage: Heat to 100-120℃, corresponding to saturated vapor pressure of 0.1-0.3 MPa, control the stirring speed to 20-40 rpm, and keep warm for 1-2 hours; so that the crystal nuclei are generated gently, and the composite crystal guide agent is fully adsorbed on the crystal edges to achieve preliminary rounding and avoid crystal nuclei breakage and agglomeration.

[0040] (2) Uniform growth stage: Heat to 125-150℃, corresponding to a saturated vapor pressure of 0.35-0.8 MPa, and simultaneously increase the stirring speed to 40-60 rpm, and keep warm for 1-2 hours; ensure uniform mass transfer and temperature of the system, and promote the regular growth of hexagonal columnar morphology.

[0041] (3) Crystallization and densification stage: Heat to 155-180℃, corresponding to a saturated vapor pressure of 0.85-1.2 MPa, and simultaneously increase the stirring speed to 60-80 rpm, and keep warm for 2-3 hours. Enhance fluid convection inside the reactor to improve crystallization integrity and particle surface smoothness.

[0042] This gradient control process conforms to the actual operating conditions of industrial reactors, and can effectively control the crystal form, prevent particle aggregation, and produce self-lubricating magnesium hydroxide with uniform morphology and smooth edges.

[0043] Specifically, the silane coupling agent is at least one of vinyltrimethoxysilane and vinyltriethoxysilane; The amount of silane coupling agent added is 0.8%-2.5% of the mass of the magnesium hydroxide matrix, and it is bonded to the powder surface of the magnesium hydroxide matrix by Si-O-Mg chemical bonds.

[0044] A self-lubricating magnesium hydroxide, wherein the self-lubricating magnesium hydroxide is prepared by the preparation method described in this invention; The self-lubricating magnesium hydroxide has a hexagonal prism shape with a sheet diameter of 0.5-5 μm, a thickness-to-diameter ratio of 0.1-0.3, and smooth rounded corners without sharp edges.

[0045] An application of magnesium hydroxide with self-lubricating function, wherein the magnesium hydroxide with self-lubricating function is used as a flame-retardant filler in cable material.

[0046] Specifically, the magnesium hydroxide is used as a halogen-free flame-retardant filler for silane self-crosslinking low-smoke halogen-free flame-retardant cable material, which can significantly improve the extrusion processing speed and reduce the die head pressure. At the same time, it does not adsorb catalysts, consume free radicals, or affect the crosslinking degree, mechanical properties, and electrical insulation properties of the material.

[0047] I. Examples of Preparation of Modified Magnesium Hydroxide Example 1 The preparation method of a self-lubricating magnesium hydroxide is as follows: (1) Prepare an aqueous solution of magnesium chloride with a Mg²⁺ concentration of 1.0 mol / L; add a composite crystal guide with a theoretical yield of 1.2 wt% of magnesium hydroxide matrix, and stir until homogeneous; The composite crystal form guide, by weight, comprises: 40 parts of organophosphonate (PAPEMP), 30 parts of polyether polyol (PEG-4000), and 20 parts of low molecular weight alkyl sulfonate (SDBS).

[0048] (2) Slowly add NaOH aqueous solution (10% by mass) to adjust the pH to 10.2, react at 50℃ for 60 min to obtain magnesium hydroxide precursor slurry; (3) Hydrothermal crystallization treatment of magnesium hydroxide precursor slurry: Nucleation-controlled angle stage: Heat to 100℃, corresponding to a saturated vapor pressure of 0.1MPa, control the stirring speed at 40 rpm, and hold for 2 hours; Uniform growth stage: Heat to 125℃, corresponding to a saturated vapor pressure of 0.35 MPa, stir at 60 rpm, and hold for 2 h; Crystallization and densification stage: Heat to 165℃, corresponding to a saturated vapor pressure of 1.0MPa, and simultaneously increase the stirring speed to 80rpm, and keep warm for 2 hours.

[0049] (4) Cool, filter, and wash until the chloride ion content is qualified (the chloride ion content in the water after washing is <0.03%); dry at 110℃ to obtain magnesium hydroxide matrix, transfer to a high-speed mixer, heat to 120℃; spray with vinyltrimethoxysilane (addition amount is 1.5wt% of the mass of magnesium hydroxide matrix), modify at high speed (1500-2000r / min) for 45min, cool and sieve to obtain self-lubricating magnesium hydroxide MH-1.

[0050] Example 2 The preparation method of a self-lubricating magnesium hydroxide is as follows: (1) Prepare an aqueous solution of magnesium sulfate with a Mg²⁺ concentration of 1.2 mol / L; add a composite crystal guide with a theoretical yield of 1.8 wt% of magnesium hydroxide matrix, and stir until homogeneous; The composite crystal form guide, by weight, comprises: 45 parts of organophosphonate (PAPEMP), 35 parts of polyether polyol (PEG-6000), and 15 parts of low molecular weight alkyl sulfonate (SDS).

[0051] (2) Add ammonia water to adjust the pH to 10.5, react at 45℃ for 80 min to obtain magnesium hydroxide precursor slurry; (3) Hydrothermal crystallization treatment of magnesium hydroxide precursor slurry: Nucleation-controlled angle stage: Heat to 120℃, corresponding to a saturated vapor pressure of 0.3MPa, control the stirring speed at 20 rpm, and hold for 1.0 h; Uniform growth stage: Heat to 150℃, corresponding to a saturated vapor pressure of 0.8 MPa, stir at 40 rpm, and hold for 1 hour; Crystallization and densification stage: Heat to 180℃, corresponding to a saturated vapor pressure of 1.2MPa, and simultaneously increase the stirring speed to 80rpm, and keep warm for 2 hours.

[0052] (4) Cool, filter, and wash until sulfate ions are qualified (sulfate ion content in the water after washing is <0.03%); dry at 110℃ to obtain magnesium hydroxide matrix, transfer to a high-speed mixer, heat to 125℃; spray with vinyltriethoxysilane (addition amount is 2.0wt% of the mass of magnesium hydroxide matrix), modify at high speed for 50min, cool and sieve to obtain self-lubricating magnesium hydroxide MH-2.

[0053] Example 3 The preparation method of a self-lubricating magnesium hydroxide is as follows: (1) Prepare an aqueous solution of magnesium sulfate with a Mg²⁺ concentration of 1.0 mol / L; add a composite crystal guide with a theoretical yield of 0.5 wt% of magnesium hydroxide matrix, and stir until homogeneous; The composite crystal form guide, by weight, comprises: 30 parts of organophosphonate (HEDP), 20 parts of polyether polyol (PPG-2000), and 10 parts of low molecular weight alkyl sulfonate (sodium p-toluenesulfonate). (2) Add ammonia water to adjust the pH to 9.5, react at 40℃ for 60 min to obtain magnesium hydroxide precursor slurry; (3) Hydrothermal crystallization treatment of magnesium hydroxide precursor slurry: Nucleation-controlled angle stage: Heat to 110℃, corresponding to a saturated vapor pressure of 0.2MPa, control the stirring speed at 30 rpm, and hold for 1.0 h; Uniform growth stage: heat to 140℃, corresponding to a saturated vapor pressure of 0.6 MPa, stir at 50 rpm, and hold for 1.5 h; Crystallization and densification stage: Heat to 155℃, corresponding to a saturated vapor pressure of 0.85MPa, and simultaneously increase the stirring speed to 80rpm, and keep warm for 3 hours.

[0054] (4) Cool, filter, and wash until sulfate ions are qualified (sulfate ion content in the water after washing is <0.03%); dry at 100℃ to obtain magnesium hydroxide matrix, transfer to a high-speed mixer, heat to 100℃; spray with vinyltrimethoxysilane (addition amount is 0.8wt% of the mass of magnesium hydroxide matrix), modify at high speed for 60min, cool and sieve to obtain self-lubricating magnesium hydroxide MH-3.

[0055] Example 4 The preparation method of a self-lubricating magnesium hydroxide is as follows: (1) Prepare an aqueous solution of magnesium sulfate with a Mg²⁺ concentration of 1.0 mol / L; add a composite crystal guide with a theoretical yield of 1.75 wt% of magnesium hydroxide matrix, and stir until homogeneous; The composite crystal form guide, by weight, comprises: 40 parts of organophosphonate (ATMP), 30 parts of polyether polyol (PEG-2000), and 20 parts of low molecular weight alkyl sulfonate (sodium p-toluenesulfonate). (2) Add ammonia water to adjust the pH to 10.2, react at 50℃ for 60 min to obtain magnesium hydroxide precursor slurry; (3) Hydrothermal crystallization treatment of magnesium hydroxide precursor slurry: Nucleation-controlled angle stage: heat to 110℃, corresponding to a saturated vapor pressure of 0.2MPa, control the stirring speed at 40 rpm, and hold for 1.0 h; Uniform growth stage: heat to 150℃, corresponding to a saturated vapor pressure of 0.8MPa, stir at 50 rpm, and hold for 1.0 h; Crystallization and densification stage: Heat to 165℃, corresponding to a saturated vapor pressure of 1.0MPa, and simultaneously increase the stirring speed to 80rpm, and keep warm for 2.5 h.

[0056] (4) Cool, filter, and wash until sulfate ions are qualified (sulfate ion content in the water after washing is <0.03%); dry at 110℃ to obtain magnesium hydroxide matrix, transfer to a high-speed mixer, heat to 115℃; spray with vinyltrimethoxysilane (addition amount is 1.65wt% of the mass of magnesium hydroxide matrix), modify at high speed for 45min, cool and sieve to obtain self-lubricating magnesium hydroxide MH-4.

[0057] Example 5 The preparation method of a self-lubricating magnesium hydroxide is as follows: (1) Prepare an aqueous solution of magnesium sulfate with a Mg²⁺ concentration of 1.0 mol / L; add a composite crystal guide with a theoretical yield of 3.0 wt% of magnesium hydroxide matrix, and stir until homogeneous; The composite crystal form guide, by weight, comprises: 50 parts of organophosphonate (PAPEMP), 40 parts of polyether polyol (PEG-4000), and 30 parts of low molecular weight alkyl sulfonate (SDS). (2) Add ammonia water to adjust the pH to 11.0, react at 60℃ for 60 min to obtain magnesium hydroxide precursor slurry; (3) Hydrothermal crystallization treatment of magnesium hydroxide precursor slurry: Nucleation-controlled angle stage: Heat to 120℃, corresponding to a saturated vapor pressure of 0.3MPa, control the stirring speed at 40 rpm, and hold for 1.0 h; Uniform growth stage: The temperature was raised to 140℃, corresponding to a saturated vapor pressure of 0.6MPa, the stirring speed was 50 rpm, and the temperature was maintained for 1.0 h; Crystallization and densification stage: Heat to 165℃, corresponding to a saturated vapor pressure of 1.0MPa, and simultaneously increase the stirring speed to 80rpm, and keep warm for 2.5 h.

[0058] (4) Cool, filter, and wash until sulfate ions are qualified (sulfate ion content in the water after washing is <0.03%); dry at 120℃ to obtain magnesium hydroxide matrix, transfer to a high-speed mixer, heat to 130℃; spray with vinyltrimethoxysilane (addition amount is 2.5wt% of the mass of magnesium hydroxide matrix), modify at high speed for 30min, cool and sieve to obtain self-lubricating magnesium hydroxide MH-5.

[0059] Example 6 The preparation method of a self-lubricating magnesium hydroxide is as follows: (1) Prepare an aqueous solution of magnesium chloride with a Mg²⁺ concentration of 1.0 mol / L; add a composite crystal guide with a theoretical yield of 1.2 wt% of magnesium hydroxide matrix, and stir until homogeneous; The composite crystal form guide, by weight, comprises: 30 parts of organophosphonate (PAPEMP), 40 parts of polyether polyol (PEG-4000), and 20 parts of low molecular weight alkyl sulfonate (SDS).

[0060] (2) Slowly add NaOH aqueous solution (10% by mass) to adjust the pH to 10.2, react at 50℃ for 60 min to obtain magnesium hydroxide precursor slurry; (3) Hydrothermal crystallization treatment of magnesium hydroxide precursor slurry: Nucleation-controlled angle stage: Heat to 100℃, corresponding to a saturated vapor pressure of 0.1MPa, control the stirring speed at 40 rpm, and hold for 2 hours; Uniform growth stage: Heat to 125℃, corresponding to a saturated vapor pressure of 0.35 MPa, stir at 60 rpm, and hold for 2 h; Crystallization and densification stage: Heat to 165℃, corresponding to a saturated vapor pressure of 1.0MPa, and simultaneously increase the stirring speed to 80rpm, and keep warm for 2 hours.

[0061] (4) Cool, filter, and wash until the chloride ion content is qualified (the chloride ion content in the water after washing is <0.03%); dry at 110℃ to obtain magnesium hydroxide matrix, transfer to a high-speed mixer, heat to 120℃; spray with vinyltrimethoxysilane (addition amount is 1.5wt% of the mass of magnesium hydroxide matrix), modify at high speed for 45min, cool and sieve to obtain self-lubricating magnesium hydroxide MH-6.

[0062] Example 7 The preparation method of a self-lubricating magnesium hydroxide is as follows: (1) Prepare an aqueous solution of magnesium chloride with a Mg²⁺ concentration of 1.0 mol / L; add a composite crystal guide with a theoretical yield of 1.2 wt% of magnesium hydroxide matrix, and stir until homogeneous; The composite crystal form guide, by weight, comprises: 40 parts of organophosphonate (PAPEMP), 40 parts of polyether polyol (PEG-4000), and 10 parts of low molecular weight alkyl sulfonate (SDS).

[0063] (2) Slowly add NaOH aqueous solution (10% by mass) to adjust the pH to 10.2, react at 50℃ for 60 min to obtain magnesium hydroxide precursor slurry; (3) Hydrothermal crystallization treatment of magnesium hydroxide precursor slurry: Nucleation-controlled angle stage: Heat to 100℃, corresponding to a saturated vapor pressure of 0.1MPa, control the stirring speed at 40 rpm, and hold for 2 hours; Uniform growth stage: Heat to 125℃, corresponding to a saturated vapor pressure of 0.35 MPa, stir at 60 rpm, and hold for 2 h; Crystallization and densification stage: Heat to 165℃, corresponding to a saturated vapor pressure of 1.0MPa, and simultaneously increase the stirring speed to 80rpm, and keep warm for 2 hours.

[0064] (4) Cool, filter, and wash until the chloride ion content is qualified (the chloride ion content in the water after washing is <0.03%); dry at 110℃ to obtain magnesium hydroxide matrix, transfer to a high-speed mixer, heat to 120℃; spray with vinyltrimethoxysilane (addition amount is 1.5wt% of the mass of magnesium hydroxide matrix), modify at high speed for 45min, cool and sieve to obtain self-lubricating magnesium hydroxide MH-7.

[0065] Comparative Example 1 Commercially available hexagonal flake magnesium hydroxide, with a silane modifier (vinyltrimethoxysilane) added at 1.5 wt% of the mass of the hexagonal flake magnesium hydroxide, is designated as DH-1.

[0066] Comparative Example 2 Conventional hexagonal flake magnesium hydroxide, modified with silane and double-coated with stearic acid, is designated DH-2.

[0067] The first step is silane modification treatment: the amount of vinyltrimethoxysilane added is 1.5wt% of the mass of hexagonal flake magnesium hydroxide. The specific operation method is as follows: place the conventional hexagonal flake magnesium hydroxide in a high-speed mixer, heat it to 120℃, spray in vinyltrimethoxysilane, and modify it at high speed for 45min at 2000r / min.

[0068] The second step is stearic acid coating treatment: the amount of stearic acid added is 0.5 wt% of the mass of the hexagonal flake magnesium hydroxide. The specific operation method is as follows: based on the first step, stearic acid is added while maintaining the temperature at 120℃, and high-speed modification is carried out at 2000 r / min for 40 min. After cooling and sieving, hexagonal flake magnesium hydroxide with silane modification and stearic acid double coating is obtained.

[0069] Comparative Example 3 Modified magnesium hydroxide was prepared using the same method as in Example 1, except that no organophosphonate was added to the composite crystal form guide in Comparative Example 3. The modified magnesium hydroxide prepared in this comparative example is designated as DH-3.

[0070] Comparative Example 4 Modified magnesium hydroxide was prepared using the same method as in Example 1, except that no polyether polyol was added to the composite crystal guide in Comparative Example 4. The modified magnesium hydroxide prepared in this comparative example is denoted as DH-4.

[0071] Comparative Example 5 Modified magnesium hydroxide was prepared using the same method as in Example 1, except that no low-molecular-weight alkyl sulfonate was added to the composite crystal guide in Comparative Example 5. The modified magnesium hydroxide prepared in this comparative example is designated as DH-5.

[0072] Comparative Example 6 Modified magnesium hydroxide was prepared using the same method as in Example 1, except that gradient heating hydrothermal crystallization was not used in the preparation process of Comparative Example 6. The hydrothermal crystallization conditions of Comparative Example 6 were as follows: At a temperature of 165℃, corresponding to a saturated vapor pressure of 1.0 MPa, a stirring speed of 80 rpm, and a holding time of 6 h, the modified magnesium hydroxide prepared in this comparative example is designated as DH-6.

[0073] Comparative Example 7 Modified magnesium hydroxide was prepared using the same method as in Example 1, except that: in the preparation process of Comparative Example 7, gradient heating hydrothermal crystallization treatment was not used. The hydrothermal crystallization treatment conditions of Comparative Example 7 were as follows: First, heat to 100℃, corresponding to a saturated vapor pressure of 0.1MPa, control the stirring speed at 40 rpm, and keep warm for 2 hours; The temperature was then raised to 165℃, corresponding to a saturated vapor pressure of 1.0 MPa, while simultaneously increasing the stirring speed to 80 rpm and holding at this temperature for 4 hours. The modified magnesium hydroxide prepared in this comparative example is designated as DH-7.

[0074] Comparative Example 8 Modified magnesium hydroxide was prepared using the same method as in Example 1, except that gradient heating hydrothermal crystallization was not used in the preparation process of Comparative Example 8. The hydrothermal crystallization conditions of Comparative Example 8 were as follows: First, heat to 125℃, corresponding to a saturated vapor pressure of 0.35MPa, control the stirring speed at 60 rpm, and keep warm for 4 hours; The temperature was then raised to 165℃, corresponding to a saturated vapor pressure of 1.0 MPa, while simultaneously increasing the stirring speed to 80 rpm and holding at this temperature for 2 hours. The modified magnesium hydroxide prepared in this comparative example is designated as DH-8.

[0075] II. Application Performance Testing The modified magnesium hydroxide obtained from the above examples and comparative examples was applied to cable materials for performance testing.

[0076] Application system: Silane self-crosslinking low-smoke halogen-free flame-retardant cable material.

[0077] The formulation of the application system, by weight, is as follows: 100 parts of PE / EVA matrix (PE is ExxonMobil's 3518CB, EVA is Yangzi Petrochemical's V6110M, and the mass ratio of PE to EVA is 2:5), 150 parts of modified magnesium hydroxide, 0.3 parts of antioxidant 1010, 0.1 parts of antioxidant 168, 2 parts of vinylsilane, 0.05 parts of organotin catalyst, 0.8 parts of PE wax, and 0.8 parts of silicone masterbatch.

[0078] The specific preparation process is as follows: Premixing: The PE / EVA matrix, vinyl silane, organotin catalyst, antioxidant 1010, and antioxidant 168 from the above materials are put into a mixer and mixed at 170°C for 20 minutes. After mixing, the materials are poured into a twin-screw extruder and the extruder temperature is set to 180°C to achieve silane grafting and granulation.

[0079] Further blending, filling, and extrusion: Modified magnesium hydroxide and lubricant (PE wax and silicone masterbatch) are added to the above grafted granules. Following the premixing process parameters, the mixture is uniformly blended and granulated to obtain cable material granules. The extruder pressure and torque values ​​are observed and recorded during the extrusion process.

[0080] Crosslinking: The cable material and copper core are extruded together and formed. The cable sheath is 1mm thick. The extrusion length and corresponding extrusion time are recorded. After forming, the cable is boiled in 90℃ warm water for 5 hours to complete the crosslinking.

[0081] The performance testing of cable materials involves the following testing methods: (1) The calculation method for extrusion pressure reduction rate is as follows: [(Extrusion pressure of Comparative Example 1 - Extrusion pressure value of corresponding embodiment or comparative example) / Extrusion pressure of Comparative Example 1] * 100%.

[0082] (2) Formula for calculating the outgoing line speed: Outgoing line length / Outgoing line time.

[0083] (3) Peel off the cross-linked cable sheath, cut standard strips according to GB / T 1040.3-2006, and conduct tensile performance tests according to the test conditions specified in GB / T32129-2015.

[0084] (4) The cable material particles that have been blended, filled and extruded into granules are placed on a flat vulcanizing machine and hot-pressed into 3mm samples at 180℃ and 16MPa. According to GB / T2406.2-2009, they are cut into standard strips by a pneumatic punching machine and tested for oxygen index according to GB / T2406.2-2009.

[0085] The specific test results are shown in Table 1 below.

[0086] Table 1 Performance Test Results

[0087] The data above show that the modified magnesium hydroxide prepared by the method described in this invention is a magnesium hydroxide product with hexagonal columnar shape, rounded corners, self-lubrication, and high cross-linking compatibility. The samples in each embodiment can significantly reduce extrusion pressure and improve processing fluidity without interfering with the silane self-cross-linking reaction. The mechanical properties, flame retardant properties, and electrical insulation properties all maintain excellent levels. Figure 1 This is a SEM image of the self-lubricating magnesium hydroxide prepared in Example 1. Figure 1 It can be seen that the magnesium hydroxide of this application has a hexagonal columnar crystal morphology with a diameter-to-thickness ratio of 4-10, and the hexagonal positions are arc-shaped with an arc angle of 75°-80°. Figure 2 The image shows the SEM morphology of magnesium hydroxide prepared in Comparative Example 1. Figure 2 It can be seen that the magnesium hydroxide prepared in the comparative example has a hexagonal plate-like crystal morphology with distinct rhomboid edges and a diameter-to-thickness ratio of 15-20, with the hexagons being sharp edges.

[0088] Furthermore, a comparison of the experimental results from Examples 6 and 7 with Example 1 shows that a suitable ratio of organophosphonate dispersant, polyether polyol, and low-molecular-weight alkyl sulfonate is more conducive to obtaining magnesium hydroxide with excellent self-lubricating properties. As the core component for crystal formation, organophosphonate strongly adsorbs onto the (001) crystal face of magnesium hydroxide through phosphonate groups to suppress growth in the thickness direction, forcing the formation of a regular hexagonal columnar basic morphology. Polyether polyol, after moderate adsorption of organophosphonate, still needs sufficient surface area for selective adsorption onto crystal edges and vertices, achieving rounded corners by steric hindrance to passivate the growth rate. If the ratio of organophosphonate dispersant to polyether polyol is less than 1.2, insufficient organophosphonate leads to uncontrolled crystal formation (irregular thick crystals or agglomeration); if the ratio is greater than 1.5, excessive occupation of surface sites by organophosphonate hinders effective adsorption of polyether polyol, resulting in incomplete rounding. Meanwhile, the mass ratio of polyether polyol to low-molecular-weight alkyl sulfonate is limited to (1.2-2.5):1. Low-molecular-weight alkyl sulfonate promotes the synchronous generation and uniform dispersion of crystal nuclei by reducing interfacial tension, preventing particle adhesion. Polyether polyol needs to dominate adsorption on the basis of sufficient dispersion to complete the corner passivation. If the ratio is lower than 1.2, the relative excess of alkyl sulfonate will compete for adsorption and interfere with the crystal form guidance of organophosphonates and the corner rounding effect of polyether polyol. If it is higher than 2.5, insufficient alkyl sulfonate will lead to decreased dispersibility, particle agglomeration, and the polyether polyol will not be able to uniformly contact the corners of each crystal, resulting in uneven corner rounding effect. Therefore, the above ratio ensures the stepwise controllable realization of "regular hexagonal columnar crystal form - smooth corner rounding - uniform dispersion without agglomeration", thus providing a low-friction, high specific surface area, and highly dispersible magnesium hydroxide matrix for subsequent dry silane modification, and finally obtaining a self-lubricating magnesium hydroxide product with significantly improved lubrication effect.

[0089] A comparison of the experimental results of Comparative Example 1 and Example 1 shows that the lubrication effect of DH-1, which lacks a rounded corner structure, is significantly reduced in Comparative Example 1.

[0090] A comparison of the experimental results of Comparative Example 2 and Example 1 shows that DH-2 with added stearic acid in Comparative Example 2 exhibits significant cross-linking failure.

[0091] A comparison of the experimental results from Comparative Examples 3-5 and Example 1 shows that a composite crystal-directing agent, formulated with organophosphonates, polyether polyols, and low-molecular-weight alkyl sulfonates, can controllably prepare magnesium hydroxide with hexagonal columnar morphology, rounded edges, self-lubrication, and high dispersibility. When applied to silane self-crosslinking low-smoke halogen-free cable materials, this significantly reduces extrusion torque and die head pressure, increases wire output speed, and does not affect crosslinking efficiency, mechanical properties, or electrical insulation performance. If any one of the organophosphonates, polyether polyols, or low-molecular-weight alkyl sulfonates is missing, the synergistic control of the hexagonal columnar morphology and rounded edges cannot be achieved.

[0092] A comparison of the experimental results of Comparative Examples 6-8 and Example 1 shows that without a suitable gradient heating hydrothermal crystallization treatment, the morphology control of magnesium hydroxide is limited, and magnesium hydroxide particles are prone to aggregation. This affects the self-lubricating properties of the final magnesium hydroxide and also causes the composite crystal guide to be encapsulated in the magnesium hydroxide, which cannot be removed by conventional washing processes. Ultimately, this results in residual composite crystal guide in the magnesium hydroxide, which also affects the flame retardant effect of magnesium hydroxide in cable materials.

[0093] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0094] For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for preparing magnesium hydroxide with self-lubricating function, characterized in that, The preparation method is as follows: S1. Prepare an aqueous solution of magnesium salt, add a composite crystal form guide, and mix thoroughly; the composite crystal form guide comprises 30-50 parts of organophosphonate dispersant, 20-40 parts of polyether polyol, and 10-30 parts of low molecular weight alkyl sulfonate by weight. The mass ratio of organophosphonate dispersant to polyether polyol is (1.2-1.5):1; The mass ratio of polyether polyol to low molecular weight alkyl sulfonate is (1.2-2.5):1; S2. Add alkaline precipitant to adjust pH to weakly alkaline, carry out precipitation reaction, and obtain magnesium hydroxide precursor slurry; S3. The precursor slurry is subjected to gradient heating hydrothermal crystallization treatment. S4. The product of hydrothermal crystallization treatment is separated into solid and liquid, washed and dried to obtain magnesium hydroxide matrix. The magnesium hydroxide matrix is ​​modified with silane coupling agent by dry method to obtain magnesium hydroxide with self-lubricating function. In step S3, the gradient heating hydrothermal crystallization treatment includes the following processes in sequence: (1) Nucleation control angle stage: heat up to 100-120℃, corresponding to a saturated vapor pressure of 0.1-0.3 MPa, control the stirring speed at 20-40 rpm, and keep warm for 1-2 h; (2) Uniform growth stage: Heat to 125-150℃, corresponding to a saturated vapor pressure of 0.35-0.8 MPa, and simultaneously increase the stirring speed to 40-60 rpm, and keep warm for 1-2 h; (3) Crystallization and densification stage: Heat to 155-180℃, corresponding to a saturated vapor pressure of 0.85-1.2 MPa, and simultaneously increase the stirring speed to 60-80 rpm, and keep warm for 2-3 h.

2. The method for preparing magnesium hydroxide with self-lubricating function according to claim 1, characterized in that, The amount of the composite crystal guide agent added is 0.5%-3.0% of the theoretical mass of the magnesium hydroxide matrix.

3. The method for preparing magnesium hydroxide with self-lubricating function according to claim 1, characterized in that, In step S2, an alkaline precipitant is added dropwise to adjust the pH to 9.5-11.0, and a precipitation reaction is carried out at 20-60℃ to obtain magnesium hydroxide precursor slurry.

4. The method for preparing magnesium hydroxide with self-lubricating function according to claim 1, characterized in that, The silane coupling agent is at least one of vinyltrimethoxysilane and vinyltriethoxysilane.

5. The method for preparing magnesium hydroxide with self-lubricating function according to claim 1, characterized in that, The amount of the silane coupling agent added is 0.8%-2.5% of the mass of the magnesium hydroxide matrix.

6. A magnesium hydroxide with self-lubricating function, characterized in that, The self-lubricating magnesium hydroxide is prepared by the preparation method described in any one of claims 1-5; The self-lubricating magnesium hydroxide has a hexagonal prism shape with a sheet diameter of 0.5-5 μm, a thickness-to-diameter ratio of 0.1-0.3, and smooth rounded corners without sharp edges.

7. An application of magnesium hydroxide with self-lubricating function according to claim 6, characterized in that, The self-lubricating magnesium hydroxide is used as a flame-retardant filler in cable material.

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