A modified magnesium hydroxide powder and its preparation method and application

Abstract

The present invention relates to the field of inorganic material technology, and provides a modified magnesium hydroxide powder, a preparation method thereof, and an application thereof. The preparation method provided by the present invention comprises the following steps: crushing brucite ore, wet ball milling, vibration screening, air separation and classification, and surface modification treatment in sequence to obtain modified magnesium hydroxide powder; the reagent used for the surface modification treatment is a pre-hydrolyzed silane coupling agent. The present invention combines wet ball milling, vibration screening, and air separation and classification to solve the problem of wide particle size distribution of magnesium hydroxide powder prepared by traditional physical grinding methods, such as rolling mills, air flow mills, wet stirred mills, ring roller mills, etc., and also solves the problems of high energy consumption, wide particle size distribution, and large breakpoints when using a single air separation and classification method. The present invention uses a pre-hydrolyzed silane coupling agent, which can achieve uniform coating of the magnesium hydroxide powder with the silane coupling agent and improve its compatibility with the resin substrate.

Description

Technical Field

[0001] The present invention relates to the technical field of inorganic materials, and in particular to modified magnesium hydroxide powder, a preparation method and application thereof. Background Art

[0002] The thermal conductivity of pure nylon PA66 and PA6 resins is generally around 0.3 W / m·K. By adding a high proportion of thermally conductive fillers to the resin, the thermal conductivity of nylon materials can be increased to 0.5-1.0 W / m·K, thereby improving the material's thermal conductivity and making these nylon materials widely used in the emerging field of LED lighting.

[0003] Commonly used thermally conductive fillers include inorganic materials such as boron nitride, aluminum nitride, magnesium hydroxide, aluminum hydroxide, aluminum oxide, and graphite, in various shapes, including granular, flake, spherical, and fibrous. When the filler content in a resin reaches a critical value, the fillers can form a network-like or chain-like structure within the resin system through contact and interaction, forming a heat transfer channel. When heat flows through the material, the heat is dissipated through the internal thermal network in a phonon-like manner, thereby improving the material's thermal conductivity.

[0004] As a low-cost inorganic thermal conductive filler, magnesium hydroxide can not only form a good physically connected thermal conductive network structure in PA6 and improve the thermal conductivity of polymer materials, but magnesium hydroxide is also a halogen-free and environmentally friendly flame retardant with good smoke suppression effect, which can solve the problem of low limiting oxygen index and flammability of polymer materials.

[0005] At present, the market mostly adopts the method of mechanical grinding of brucite to prepare magnesium hydroxide powder. This method has low processing cost, is green and environmentally friendly, has a simple process flow, and has broad market prospects. Commonly used grinding equipment includes rolling mill, air flow mill, stirred mill, ring roller mill, etc. The mechanical grinding method usually uses the high-speed shearing, collision or crushing effect of the above-mentioned grinding equipment to prepare magnesium hydroxide powder, but the prepared magnesium hydroxide powder has a wide particle size distribution and a large breakpoint. Among them, coarse particles (D 97 ≥30μm) will lead to the problem of rough surface of the final product when modifying the thermal conductivity of nylon, and the surface of the product will have pits, cracks and other undesirable phenomena; fine particles (D 97≤10μm) will lead to difficulties in cutting and increasing processing difficulty in actual application. At the same time, the presence of particles that are too large or too small will also cause the magnesium hydroxide particles to be unable to form a continuous and uniform heat conduction channel in the nylon resin matrix, affecting the thermal conductivity of the modified nylon. In addition, in order to further improve the compatibility of magnesium hydroxide with the nylon resin matrix, the magnesium hydroxide powder needs to be surface coated and modified. Traditional dry modification methods, such as mechanical and chemical force modification methods, have disadvantages such as high energy consumption and uneven surface coating; wet surface modification mainly uses chemical reaction methods for modification, which is complex, costly, and prone to pollution.

[0006] Existing production methods and their combination make it difficult to obtain magnesium hydroxide powder with uniform particle distribution, narrow particle size distribution and strong bonding with the nylon resin matrix through a simple process flow. Summary of the Invention

[0007] In view of this, the present invention provides a modified magnesium hydroxide powder and its preparation method and application. The preparation method provided by the present invention has a simple process, and the obtained modified magnesium hydroxide powder has uniform particle distribution, narrow particle size distribution, and strong binding force with nylon resin.

[0008] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0009] A method for preparing modified magnesium hydroxide powder comprises the following steps:

[0010] The brucite ore is sequentially subjected to crushing, wet ball milling, vibration screening, air separation classification and surface modification treatment to obtain modified magnesium hydroxide powder;

[0011] The reagent used for the surface modification treatment is a pre-hydrolyzed silane coupling agent;

[0012] The particle size of the modified magnesium hydroxide powder meets the following conditions: 50 14~19μm, D 97 20~25μm, D 100 The particle size of the modified magnesium hydroxide powder is 27 to 30 μm, and the activation degree of the modified magnesium hydroxide powder is ≥95%.

[0013] Preferably, the mass fraction of MgO in the brucite ore is ≥58%, and the fineness of the powder obtained by wet ball milling is D 97 ≤30μm.

[0014] Preferably, the equipment used for the vibration screening is an ultrasonic vibration screen, the mesh size of the screen used for the vibration screening is 400 meshes, and the vibration frequency of the vibration screening is 30 to 60 Hz.

[0015] Preferably, the equipment used for the air separation and classification is a vertical air flow classifier, and the rotation speed of the equipment during the air separation and classification is 900-1350 r / min.

[0016] Preferably, the surface modification treatment is to mix the pre-hydrolyzed silane coupling agent and the magnesium hydroxide obtained by air classification, and the particle size of the magnesium hydroxide obtained by air classification is 10 to 30 μm; the temperature of the surface modification treatment is 90° C. to 120° C., and the time of the surface modification treatment is 30 min to 60 min.

[0017] Preferably, the preparation method of the pre-hydrolyzed silane coupling agent comprises the following steps: mixing a silane coupling agent, an ethanol aqueous solution and a pH adjuster, and then performing a pre-hydrolysis reaction to obtain the pre-hydrolyzed silane coupling agent.

[0018] Preferably, the prehydrolysis reaction is carried out under stirring, and the stirring speed is 10 to 30 r / min; the temperature of the prehydrolysis reaction is room temperature, and the time of the prehydrolysis reaction is 2 to 4 hours.

[0019] Preferably, the silane coupling agent used to prepare the pre-hydrolyzed silane coupling agent includes at least one of γ-ureidopropyltriethoxysilane, γ-mercaptopropyltriethoxysilane, γ-(3,2-epoxypropyl)methyltrimethoxysilane, γ-aminopropyltriethoxysilane and γ-(ethylenediamino)propyltrimethoxysilane;

[0020] The mass of the silane coupling agent used to prepare the pre-hydrolyzed silane coupling agent is 0.8% to 1.5% of the mass of the magnesium hydroxide obtained by air separation and classification.

[0021] The present invention also provides a modified magnesium hydroxide powder prepared by the preparation method of the above scheme, wherein the particle size of the modified magnesium hydroxide powder meets the following conditions: D 50 14~19μm, D 97 20~25μm, D 100 The particle size of the modified magnesium hydroxide powder is 27 to 30 μm, and the activation degree of the modified magnesium hydroxide powder is ≥95%.

[0022] The present invention also provides the use of the modified magnesium hydroxide powder described in the above solution in thermal conductive nylon.

[0023] The present invention provides a method for preparing magnesium hydroxide powder, comprising the following steps: sequentially crushing brucite ore, wet ball milling, vibratory screening, air separation classification, and surface modification treatment to obtain magnesium hydroxide powder; the reagent used for the surface modification treatment is a pre-hydrolyzed silane coupling agent, and the particle size of the magnesium hydroxide powder meets the following conditions: D 50 14~19μm, D 97 20~25μm, D100 The magnesium hydroxide powder has a particle size of 27 to 30 μm, and the activation degree of the magnesium hydroxide powder is ≥95%. The present invention combines wet ball milling, vibratory screening, and air separation classification to solve the problem of wide particle size distribution of magnesium hydroxide powder prepared by traditional physical grinding methods such as roller mills, air flow mills, wet stirred mills, and ring roller mills. It also solves the problems of high energy consumption, wide particle size distribution, and large breakpoints in the use of a single air separation classification method. The present invention uses a pre-hydrolyzed silane coupling agent to achieve uniform coating of the magnesium hydroxide powder with the silane coupling agent, thereby improving its compatibility with the resin substrate.

[0024] Furthermore, the present invention can obtain magnesium hydroxide fractions with more uniform particle distribution and narrow particle size distribution by adjusting the particle size of wet ball milling, vibration screening and air classification conditions.

[0025] Furthermore, the present invention can achieve uniform coating and firm bonding of the magnesium hydroxide powder with the silane coupling agent by adjusting the type of silane coupling agent and the pre-hydrolysis conditions, thereby improving the compatibility and dispersibility of the magnesium hydroxide powder in the nylon resin matrix, and is beneficial to improving the mechanical properties of the nylon resin matrix.

[0026] The present invention also provides magnesium hydroxide powder prepared by the preparation method of the above scheme, wherein the particle size of the magnesium hydroxide powder meets the following conditions: D 50 14~19μm, D 97 20~25μm, D 100 The magnesium hydroxide powder has a particle size of 27 to 30 μm and an activation degree of ≥95%. The magnesium hydroxide powder prepared by the invention has uniform particle distribution, narrow particle size distribution and high activation degree.

[0027] The present invention also provides the use of the magnesium hydroxide powder prepared by the preparation method described above in the preparation of thermally conductive nylon. Because the magnesium hydroxide powder prepared by the preparation method of the present invention has uniform particle distribution, narrow particle size distribution, and high activation, it can form a good bond with the nylon resin matrix, which is beneficial for improving the flame retardancy and mechanical properties of the nylon resin. Therefore, it is very suitable for use in the preparation of thermally conductive nylon. DETAILED DESCRIPTION

[0028] The present invention provides a method for preparing magnesium hydroxide powder, comprising the following steps:

[0029] The brucite ore is sequentially subjected to crushing, wet ball milling, vibration screening, air separation classification and surface modification treatment to obtain magnesium hydroxide powder;

[0030] The reagent used for the surface modification treatment is a pre-hydrolyzed silane coupling agent, and the particle size of the magnesium hydroxide powder meets the following conditions: D 50 14~19μm, D 9720~25μm, D 100 The particle size is 27 to 30 μm, and the activation degree of the magnesium hydroxide powder is ≥95%.

[0031] Unless otherwise specified, the raw materials used in the present invention are all commercially available.

[0032] The present invention sequentially subjects brucite ore to crushing, wet ball milling, vibratory screening, air separation classification, and surface modification to produce magnesium hydroxide powder. In the present invention, the mass fraction of MgO in the brucite ore is preferably ≥58%, more preferably 58-65%, and even more preferably 60-62%. In the present invention, the crushing preferably includes sequentially performing cleaning, coarse crushing, primary crushing, and secondary crushing. In the present invention, the cleaning preferably includes washing the brucite ore with water, preferably high-pressure water washing; the coarse crushing includes crushing the washed brucite ore into lumps with a particle size of 5-10 cm; the primary crushing includes crushing the material obtained from the coarse crushing into particles with a particle size of 1-2 cm, preferably performed in a jaw crusher; and the secondary crushing includes crushing the material obtained from the primary crushing into raw slag with a particle size of 5-10 mm. In the present invention, the particle size of the raw slag obtained from the crushing is preferably 5-10 mm, more preferably 5-8 mm.

[0033] In the present invention, the wet ball milling is preferably carried out in a ball mill, and the rotation speed of the wet ball milling is preferably 60 to 140 r / min, more preferably 80 to 140 r / min, and more preferably 80 to 100 r / min; the ball-to-material ratio of the wet ball milling is preferably 1 to 6:1, more preferably 2 to 5:1, and more preferably 2 to 3:1. In the present invention, the fineness of the magnesium hydroxide powder obtained by the wet ball milling is preferably D 97 The present invention preferably uses wet ball milling to obtain powder with narrow particle size distribution and uniform particles, which is beneficial to reducing the energy consumption and difficulty of subsequent air separation and classification.

[0034] In the present invention, the equipment used for the vibration screening is preferably an ultrasonic vibration screen, the mesh size of the screen used for the vibration screening is preferably 400 mesh, and the vibration frequency of the vibration screening is preferably 30 to 60 Hz, more preferably 45 Hz. The preferred vibration screening method of the present invention is conducive to reducing the energy consumption and cost of the process. In the present invention, the particle size of the undersize powder obtained by the vibration screening is preferably ≤30 μm, and the particle size of the oversize powder is preferably >30 μm; the undersize powder is preferably subjected to the air separation classification, and the oversize powder is preferably returned to the wet ball milling step.

[0035] In the present invention, the equipment used for the air classification is preferably a vertical airflow classifier, and the rotation speed of the equipment used for the air classification is preferably 900-1350 r / min, more preferably 1000-1250 r / min, and further preferably 1050-1200 r / min. The present invention preferably sets the classification critical line of the air classification to 10 μm by controlling the frequency of the classifier. In the present invention, after the air classification, powder with a particle size of less than 10 μm is preferably classified as fine powder, and powder with a particle size of 10-30 μm is preferably classified as coarse powder; the classified fine powder is preferably collected and packaged for use as a modifier for PVC cables or PVC films, and the classified coarse powder is preferably surface-modified.

[0036] In the present invention, the reagent used for the surface modification treatment is a pre-hydrolyzed silane coupling agent, and the preparation method of the pre-hydrolyzed silane coupling agent preferably includes the following steps: mixing the silane coupling agent, an ethanol aqueous solution and a pH adjuster, and then performing a pre-hydrolysis reaction to obtain the pre-hydrolyzed silane coupling agent. In the present invention, the silane coupling agent preferably includes at least one of γ-ureidopropyltriethoxysilane, γ-mercaptopropyltriethoxysilane, γ-(3,2-epoxypropyl)methyltrimethoxysilane, γ-aminopropyltriethoxysilane and γ-(ethylenediamino)propyltrimethoxysilane, more preferably one or more of γ-aminopropyltriethoxysilane, γ-(ethylenediamino)propyltrimethoxysilane, γ-mercaptopropyltriethoxysilane and γ-ureidopropyltriethoxysilane, further preferably one or more of γ-aminopropyltriethoxysilane, γ-(ethylenediamino)propyltrimethoxysilane and γ-mercaptopropyltriethoxysilane, most preferably γ-(ethylenediamino)propyltrimethoxysilane and / or γ-mercaptopropyltriethoxysilane. In a specific embodiment of the present invention, the silane coupling agent is preferably γ-aminopropyltriethoxysilane and γ-(ethylenediamino)propyltrimethoxysilane in a mass ratio of 1:1, γ-mercaptopropyltriethoxysilane and γ-(ethylenediamino)propyltrimethoxysilane in a mass ratio of 1:1, γ-aminopropyltriethoxysilane in a mass ratio of 1:1:1, γ-mercaptopropyltriethoxysilane and γ-(ethylenediamino)propyltrimethoxysilane, γ-(ethylenediamino)propyltrimethoxysilane in a mass ratio of 1:1 and γ-(3,2-epoxypropyl)methyltrimethoxysilane, or γ-(ethylenediamino)propyltrimethoxysilane and γ-ureidopropyltriethoxysilane in a mass ratio of 1:1. In the present invention, the volume ratio of anhydrous ethanol to water in the ethanol aqueous solution is preferably 1:4-9, more preferably 1:5-8, further preferably 1:6-7, and most preferably 1:6. In the present invention, the volume ratio of the silane coupling agent to the ethanol aqueous solution is preferably 1:3-7, more preferably 1:3.5-6, and further preferably 1:4-5. The present invention preferably uses ethanol aqueous solution as the solvent for surface modification treatment, which is easy to volatilize, which is beneficial to reduce energy consumption in subsequent processes and reduce production costs. In the present invention, the pH adjuster preferably includes sodium citrate. In the present invention, the silane coupling agent, ethanol aqueous solution and pH adjuster are preferably mixed by first mixing the silane coupling agent and ethanol aqueous solution, and then slowly adding the pH adjuster to adjust the pH value of the feed solution to 7.5-8. In the present invention, the mixing is preferably carried out at room temperature, the mixing method is preferably stirring, the stirring speed is preferably 20 to 60 r / min, more preferably 30 to 50 r / min, and further preferably 45 r / min, and the mixing time is preferably 10 to 30 min, more preferably 15 to 25 min, and more preferably 20 min.In the present invention, the pre-hydrolysis reaction is preferably carried out under stirring conditions, and the stirring speed is preferably 10 to 30 r / min, more preferably 10 to 20 r / min, and further preferably 15 r / min; the temperature of the pre-hydrolysis reaction is preferably room temperature, and the pre-hydrolysis reaction time is preferably 2 to 4 hours, more preferably 2 to 3.5 hours, and further preferably 2.5 to 3 hours. The present invention preferably sets the above-mentioned pre-hydrolysis reaction conditions to facilitate the full hydrolysis of the silane coupling agent, increase its dispersibility, and thus increase the contact area with the magnesium hydroxide powder, thereby improving the surface modification effect while helping to reduce the amount of the silane coupling agent.

[0037] In the present invention, the surface modification treatment is preferably performed by mixing the pre-hydrolyzed silane coupling agent with the magnesium hydroxide obtained by air classification. The particle size of the magnesium hydroxide obtained by air classification is preferably 10 to 30 μm. In the present invention, the mass of the silane coupling agent used to prepare the pre-hydrolyzed silane coupling agent is preferably 0.8% to 1.5% of the mass of the magnesium hydroxide obtained by air classification, more preferably 0.9 to 1.3%, and even more preferably 1.0 to 1.2%.

[0038] In the present invention, the surface modification treatment is preferably carried out under stirring conditions, and the stirring is preferably carried out in a mixing mixer. The stirring speed is preferably 200-250 r / min, more preferably 215-235 r / min, and further preferably 220-230 r / min. In the present invention, the temperature of the surface modification treatment is preferably 90°C to 120°C, more preferably 100°C to 120°C, and further preferably 105°C to 115°C. In the present invention, the time of the surface modification treatment is preferably 30min to 60min, more preferably 40min to 60min, and further preferably 45min to 50min. In the present invention, the above-mentioned modification temperature and time are preferably conducive to increasing the coverage rate of the pre-hydrolyzed silane coupling agent on the magnesium hydroxide powder, thereby increasing the activation degree of the magnesium hydroxide powder obtained after modification.

[0039] In the present invention, the particle size of the modified magnesium hydroxide powder satisfies the following conditions: 50 14~19μm, D 97 20~25μm, D 100 It is 27 to 30 μm and preferably meets the following conditions: D 50 14.5~18.5μm, D 97 20.5~23.5μm, D 100 is 27.5 to 29.0 μm, and more preferably satisfies the following conditions: D 50 15.5~17.5μm, D 97 21~23μm, D 100The activation degree of the modified magnesium hydroxide powder is ≥95%, preferably 95-98%, and more preferably 96-97.5%.

[0040] The present invention also provides a modified magnesium hydroxide powder prepared by the preparation method of the above scheme, wherein the particle size of the modified magnesium hydroxide powder meets the following conditions: D 50 14~19μm, D 97 20~25μm, D 100 The particle size of the modified magnesium hydroxide powder is 27 to 30 μm, and the activation degree of the modified magnesium hydroxide powder is ≥95%.

[0041] The present invention also provides the use of the modified magnesium hydroxide powder described in the above solution in thermal conductive nylon. The present invention has no special requirements for the application, which is a method well known to those skilled in the art.

[0042] The technical solutions of the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention.

[0043] Example 1

[0044] The brucite ore with MgO content of 60wt% was washed, coarsely crushed, primary crushed and secondary crushed in sequence to obtain raw slag with a particle size of 5-8mm. The raw slag was wet-milled in a large ball mill (rotating speed of 90r / min, ball-to-material ratio of 3:1) to obtain D 97 ≤30μm magnesium hydroxide powder, the magnesium hydroxide powder is vibrated and screened (the sieve used for vibrating screening is an ultrasonic vibrating screen, the mesh number of the ultrasonic vibrating screen is 400 mesh, and the vibration frequency of the vibrating screening is preferably 45Hz), the undersize powder obtained by vibrating screening (particle size ≤30μm) is classified by a vertical air flow classifier (classification speed is 1250r / min), and the lower layer of magnesium hydroxide coarse powder (particle size is 10-30μm) after classification is collected for standby use;

[0045] Preparation of a pre-hydrolyzed silane coupling agent: Dissolve γ-aminopropyltriethoxysilane and γ-(ethylenediamino)propyltrimethoxysilane in an ethanol-water solution at a mass ratio of 1:1. The volume ratio of the silane coupling agent to the ethanol-water solution is 1:5, and the volume ratio of anhydrous ethanol to water in the ethanol-water solution is 1:9. Slowly add sodium citrate as a pH adjuster. The silane coupling agent, ethanol-water solution, and sodium citrate are mixed under stirring at room temperature at a speed of 45 rpm for 10 minutes. The pH value of the reaction system is adjusted to 7.5. Then, stir at a speed of 15 rpm for 3 hours at room temperature to obtain a pre-hydrolyzed silane coupling agent.

[0046] The pre-hydrolyzed silane coupling agent and the classified magnesium hydroxide coarse powder were surface-modified in a high-speed mixer. The mass of the silane coupling agent used to prepare the pre-hydrolyzed silane coupling agent was 1% of the mass of the magnesium hydroxide coarse powder. The stirring speed was 220 r / min, the surface modification temperature was 105° C., and the surface modification time was 45 min to obtain modified magnesium hydroxide powder.

[0047] Example 2

[0048] The brucite ore with MgO content of 60wt% was washed, coarsely crushed, primary crushed and secondary crushed in sequence to obtain raw slag with a particle size of 5-8mm. The raw slag was wet-milled in a large ball mill (rotating speed of 100r / min, ball-to-material ratio of 2:1) to obtain D 97 ≤30μm magnesium hydroxide powder, the magnesium hydroxide powder is vibrated and screened (the sieve used for vibrating screening is an ultrasonic vibrating screen, the mesh number of the ultrasonic vibrating screen is 400 mesh, and the vibration frequency of the vibrating screening is preferably 60Hz), the undersize powder obtained by vibrating screening (particle size ≤30μm) is classified by a vertical air flow classifier (classification speed is 1050r / min), and the lower layer of magnesium hydroxide coarse powder (particle size is 10-30μm) after classification is collected for standby use;

[0049] Preparation of a pre-hydrolyzed silane coupling agent: Dissolve γ-mercaptopropyltriethoxysilane and γ-(ethylenediamino)propyltrimethoxysilane in an ethanol-water solution at a mass ratio of 1:1. The volume ratio of the silane coupling agent to the ethanol-water solution is 1:4, and the volume ratio of anhydrous ethanol to water in the ethanol-water solution is 1:6. Slowly add sodium citrate. The silane coupling agent, ethanol-water solution, and sodium citrate are mixed under stirring at room temperature at a speed of 45 rpm for 30 minutes. The pH value of the reaction system is adjusted to 8.0. Then, stir at a speed of 15 rpm for 2 hours at room temperature to obtain a pre-hydrolyzed silane coupling agent.

[0050] The pre-hydrolyzed silane coupling agent and the classified magnesium hydroxide coarse powder were surface-modified in a high-speed mixer. The mass of the silane coupling agent used to prepare the pre-hydrolyzed silane coupling agent was 0.9% of the mass of the magnesium hydroxide coarse powder. The stirring speed was 220 r / min, the surface modification temperature was 105° C., and the surface modification time was 60 min to obtain modified magnesium hydroxide powder.

[0051] Example 3

[0052] The brucite ore with MgO content of 62wt% was washed, coarsely crushed, primary crushed and secondary crushed in sequence to obtain raw slag with a particle size of 5-8mm. The raw slag was wet-milled in a large ball mill (rotation speed of 90r / min, ball-to-material ratio of 2:1) to obtain D 97≤30μm magnesium hydroxide powder, the magnesium hydroxide powder is vibrated and screened (the sieve used for vibrating screening is an ultrasonic vibrating screen, the mesh number of the ultrasonic vibrating screen is 400 mesh, and the vibration frequency of the vibrating screening is preferably 45Hz), the undersize powder obtained by vibrating screening (particle size ≤30μm) is classified by a vertical air flow classifier (classification speed is 1050r / min), and the lower layer of magnesium hydroxide coarse powder (particle size is 10-30μm) after classification is collected for standby use;

[0053] Preparation of a pre-hydrolyzed silane coupling agent: Dissolve γ-aminopropyltriethoxysilane, γ-mercaptopropyltriethoxysilane, and γ-(ethylenediamino)propyltrimethoxysilane in an ethanol aqueous solution at a mass ratio of 1:1:1. The volume ratio of the silane coupling agent to the ethanol aqueous solution is 1:6, and the volume ratio of anhydrous ethanol to water in the ethanol aqueous solution is 1:9. Slowly add sodium citrate. The silane coupling agent, ethanol aqueous solution, and sodium citrate are mixed under stirring at room temperature at a speed of 45 rpm for 20 minutes. The pH value of the reaction system is adjusted to 7.5. Then, stir at a speed of 15 rpm for 2.5 hours at room temperature to obtain a pre-hydrolyzed silane coupling agent.

[0054] The pre-hydrolyzed silane coupling agent and the classified magnesium hydroxide coarse powder were surface-modified in a high-speed mixer. The mass of the silane coupling agent used to prepare the pre-hydrolyzed silane coupling agent was 1.2% of the mass of the magnesium hydroxide coarse powder. The stirring speed was 230 r / min, the surface modification temperature was 105° C., and the surface modification time was 60 min to obtain modified magnesium hydroxide powder.

[0055] Example 4

[0056] The brucite ore with MgO content of 60wt% was washed, coarsely crushed, primary crushed and secondary crushed in sequence to obtain raw slag with a particle size of 5-8mm. The raw slag was wet-milled in a large ball mill (rotating speed of 100r / min, ball-to-material ratio of 3:1) to obtain D 97 ≤30μm magnesium hydroxide powder, the magnesium hydroxide powder is vibrated and screened (the sieve used for vibrating screening is an ultrasonic vibrating screen, the mesh number of the ultrasonic vibrating screen is 400 mesh, and the vibration frequency of the vibrating screening is preferably 45Hz), the undersize powder obtained by vibrating screening (particle size ≤30μm) is classified by a vertical air flow classifier (classification speed is 1250r / min), and the lower layer of magnesium hydroxide coarse powder (particle size is 10-30μm) after classification is collected for standby use;

[0057] Preparation of a pre-hydrolyzed silane coupling agent: Dissolve γ-(ethylenediamino)propyltrimethoxysilane in an ethanol-water solution at a volume ratio of 1:5 between the silane coupling agent and the ethanol-water solution, and a volume ratio of 1:6 between anhydrous ethanol and water in the ethanol-water solution. Slowly add sodium citrate. The silane coupling agent, ethanol-water solution, and sodium citrate are mixed under stirring at room temperature at a speed of 45 rpm for 30 minutes. The pH value of the reaction system is adjusted to 8.0. The mixture is then stirred at a speed of 15 rpm for 3 hours at room temperature to obtain a pre-hydrolyzed silane coupling agent.

[0058] The pre-hydrolyzed silane coupling agent and the classified magnesium hydroxide coarse powder were surface-modified in a high-speed mixer. The mass of the silane coupling agent used to prepare the pre-hydrolyzed silane coupling agent was 1.5% of the mass of the magnesium hydroxide coarse powder. The stirring speed was 230 r / min, the surface modification temperature was 120° C., and the surface modification time was 60 min to obtain modified magnesium hydroxide powder.

[0059] Example 5

[0060] The brucite ore with MgO content of 60wt% was washed, coarsely crushed, primary crushed and secondary crushed in sequence to obtain raw slag with a particle size of 5-8mm. The raw slag was wet-milled in a large ball mill (rotation speed of 85r / min, ball-to-material ratio of 3:1) to obtain D 97 ≤30μm magnesium hydroxide powder, the magnesium hydroxide powder is vibrated and screened (the sieve used for vibrating screening is an ultrasonic vibrating screen, the mesh number of the ultrasonic vibrating screen is 400 mesh, and the vibration frequency of the vibrating screening is preferably 60Hz), the undersize powder obtained by vibrating screening (particle size ≤30μm) is classified by a vertical air flow classifier (classification speed is 1250r / min), and the lower layer of magnesium hydroxide coarse powder (particle size is 10-30μm) after classification is collected for standby use;

[0061] Preparation of a pre-hydrolyzed silane coupling agent: Dissolve γ-(ethylenediamino)propyltrimethoxysilane and γ-(3,2-epoxypropyl)methyltrimethoxysilane in an ethanol-water solution at a mass ratio of 1:1. The volume ratio of the silane coupling agent to the ethanol-water solution is 1:6, and the volume ratio of anhydrous ethanol to water in the ethanol-water solution is 1:9. Slowly add sodium citrate. The silane coupling agent, ethanol-water solution, and sodium citrate are mixed under stirring at room temperature at a speed of 45 rpm for 30 minutes. The pH value of the reaction system is adjusted to 7.5. Then, stir at a speed of 15 rpm for 3 hours at room temperature to obtain a pre-hydrolyzed silane coupling agent.

[0062] The pre-hydrolyzed silane coupling agent and the classified magnesium hydroxide coarse powder were surface-modified in a high-speed mixer. The mass of the silane coupling agent used to prepare the pre-hydrolyzed silane coupling agent was 1.2% of the mass of the magnesium hydroxide coarse powder. The stirring speed was 225 r / min, the surface modification temperature was 120° C., and the surface modification time was 45 min to obtain modified magnesium hydroxide powder.

[0063] Example 6

[0064] The brucite ore with MgO content of 60wt% was washed, coarsely crushed, primary crushed and secondary crushed in sequence to obtain raw slag with a particle size of 5-8mm. The raw slag was wet-milled in a large ball mill (rotation speed of 85r / min, ball-to-material ratio of 2:1) to obtain D 97 ≤30μm magnesium hydroxide powder, the magnesium hydroxide powder is vibrated and screened (the sieve used for vibrating screening is an ultrasonic vibrating screen, the mesh number of the ultrasonic vibrating screen is 400 mesh, and the vibration frequency of the vibrating screening is preferably 45Hz), the undersize powder obtained by vibrating screening (particle size ≤30μm) is classified by a vertical air flow classifier (classification speed is 1250r / min), and the lower layer of magnesium hydroxide coarse powder (particle size is 10-30μm) after classification is collected for standby use;

[0065] Preparation of a pre-hydrolyzed silane coupling agent: Dissolve γ-(ethylenediamino)propyltrimethoxysilane and γ-ureidopropyltriethoxysilane in an ethanol-water solution at a mass ratio of 1:1. The volume ratio of the silane coupling agent to the ethanol-water solution is 1:5, and the volume ratio of anhydrous ethanol to water in the ethanol-water solution is 1:6. Slowly add sodium citrate. The silane coupling agent, ethanol-water solution, and sodium citrate are mixed under stirring at room temperature at a speed of 45 rpm for 20 minutes. The pH value of the reaction system is adjusted to 8.0. Then, stir at a speed of 15 rpm for 3 hours at room temperature to obtain a pre-hydrolyzed silane coupling agent.

[0066] The pre-hydrolyzed silane coupling agent and the classified magnesium hydroxide coarse powder were surface-modified in a high-speed mixer. The mass of the silane coupling agent used to prepare the pre-hydrolyzed silane coupling agent was 1% of the mass of the magnesium hydroxide coarse powder. The stirring speed was 230 r / min, the surface modification temperature was 105° C., and the surface modification time was 45 min to obtain modified magnesium hydroxide powder.

[0067] Comparative Examples 1 to 3

[0068] Commercially available activated magnesium hydroxide powders were used as Comparative Examples 1, 2, and 3. Comparative Example 1 was Q-KB-2GX sold by Weifang Lihe Powder Technology Co., Ltd.; Comparative Example 2 was 2802 sold by Hefei Zhongke Flame Retardant New Materials Co., Ltd.; and Comparative Example 3 was Aitemag55 sold by Jiangsu Aitek Flame Retardant Materials Co., Ltd.

[0069] Comparative Example 4

[0070] The preparation method is basically the same as that of Example 4, except that the "pre-hydrolyzed silane coupling agent" is adjusted to "silane coupling agent", that is, the silane coupling agent is not subjected to pre-hydrolysis reaction.

[0071] The particle size of the magnesium hydroxide powders of Examples 1 to 6 and Comparative Examples 1 to 4 was measured using a BT-9300ST laser particle size analyzer produced by Liaoning Dandong Better Co., Ltd. 50 Represents the particle size value corresponding to 50% of the cumulative distribution; D 97 Represents the particle size value corresponding to 97% of the cumulative distribution; D 100 Represents the upper limit of distribution, and can also be understood as the largest particle. At the same time, the magnesium hydroxide powders of Examples 1 to 6 and Comparative Examples 1 to 4 were subjected to activation tests. The method for the activation test is as follows: weigh about 5g of sample, accurate to 0.01g; place in a separatory funnel, add 200mL of water, and shake back and forth at a speed of 120 times / min for 1min. Place it gently on the funnel stand and let it stand for 20min to 30min; after obvious stratification appears, put the sunken magnesium hydroxide into a glass sand crucible that has been dried to a constant mass at 105℃±2℃ at one time, and filter to remove water. Place in an electric constant temperature drying oven, dry at 105℃±2℃ to a constant mass, and calculate the activation degree according to Formula I.

[0072]

[0073] In formula I, m2 is the weight of the sunken magnesium hydroxide and the crucible, m1 is the weight of the crucible, and m is the amount of the sample initially weighed; the units of m2, m1 and m are all g.

[0074] The particle size distribution and activation degree test results of the magnesium hydroxide powders prepared in Examples 1 to 6 and the magnesium hydroxide powders of Comparative Examples 1 to 4 are shown in Table 1.

[0075] Table 1 Particle size distribution and activation test results of the magnesium hydroxide powders prepared in Examples 1 to 6 and Comparative Examples 1 to 4

[0076] Group <![CDATA[D 50 (μm)]]> <![CDATA[D 97 (μm)]]> <![CDATA[D 100 (μm)]]> Activation degree (%) Example 1 14.36 20.85 28.52 95.5 Example 2 16.35 22.11 29.88 96.2 Example 3 17.35 22.85 27.56 96.6 Example 4 15.69 22.65 27.86 97.3 Example 5 18.35 23.56 28.98 95.3 Example 6 14.46 20.85 27.86 96.3 Comparative Example 1 2.65 17.54 33.65 90.2 Comparative Example 2 3.90 17.38 29.72 92.1 Comparative Example 3 4.36 17.18 29.89 92.2 Comparative Example 4 16.12 23.03 27.98 94.3

[0077] As can be seen from Table 1, the magnesium hydroxide powder prepared by the preparation method of the present invention has a narrower particle size distribution and more uniform particles than existing commercial products, and at the same time has better activation, which is beneficial to improving the modification effect on nylon resin.

[0078] The magnesium hydroxide powder prepared in Examples 1 to 6 and the magnesium hydroxide powder of Comparative Examples 1 to 4 were added to PA6 as modified samples for modification. The amount of magnesium hydroxide powder was 30% of the total mass of magnesium hydroxide powder and PA6. The magnesium hydroxide powder and PA6 were added to a high-speed mixer for mixing. The mixed material was extruded and granulated using a twin-screw extruder. The granules obtained by granulation were injection molded into standard specimens in an injection molding machine, and the obtained standard specimens were subjected to performance testing. Among them, the conditions for mixing, granulating and injection molding of each modified sample and PA6 were the same. The tensile strength of the standard specimens was tested according to the GB / T1040-2006 standard, the thermal conductivity was tested according to the GB / T10297-2015 standard, and the melt index was tested according to the GB / T 3682.1-2018 standard. The performance test results of the modified PA6 prepared by the magnesium hydroxide powders prepared in Examples 1 to 6 and the magnesium hydroxide powders of Comparative Examples 1 to 4 are shown in Table 2.

[0079] Table 2 Performance test results of modified PA6 prepared from magnesium hydroxide powders prepared in Examples 1 to 6 and magnesium hydroxide powders in Comparative Examples 1 to 4

[0080] Group Tensile strength (MPa) Thermal conductivity (W / m·K) Melt index (g / 10min) Example 1 36.7 1.05 23.5 Example 2 36.5 1.03 23.6 Example 3 37.2 1.02 24.2 Example 4 35.8 1.06 23.8 Example 5 36.2 1.04 23.9 Example 6 36.4 1.03 23.7 Comparative Example 1 32.1 0.89 22.5 Comparative Example 2 33.2 0.92 21.8 Comparative Example 3 32.6 0.89 21.9 Comparative Example 4 33.6 0.92 22.8

[0081] As can be seen from Table 2, the magnesium hydroxide powder prepared by the preparation method of the present invention has a higher tensile strength, a larger thermal conductivity, and a higher melt index than the existing commercially available products. This shows that the magnesium hydroxide powder prepared by the present invention has a narrow particle size distribution, is easier to feed when applied to nylon modification, has good dispersion performance in the substrate, and has high compatibility with the substrate, which is more conducive to improving the mechanical properties, thermal conductivity and processing fluidity of the modified PA6, and is very suitable for preparing thermal conductive nylon.

[0082] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. Application of modified magnesium hydroxide powder in thermal conductive nylon, characterized in that: The preparation method of the modified magnesium hydroxide powder comprises the following steps: The brucite ore is sequentially subjected to crushing, wet ball milling, vibration screening, air separation classification and surface modification treatment to obtain modified magnesium hydroxide powder; The reagent used for the surface modification treatment is a pre-hydrolyzed silane coupling agent; the preparation method of the pre-hydrolyzed silane coupling agent comprises the following steps: mixing the silane coupling agent, an ethanol aqueous solution and a pH adjuster, and then performing a pre-hydrolysis reaction to obtain the pre-hydrolyzed silane coupling agent; The fineness of the powder obtained by wet ball milling is D 97 ≤30μm; The mesh size of the sieve used for the vibration screening is 400 mesh, and the vibration frequency of the vibration screening is 30 to 60 Hz; The rotation speed of the equipment during the air separation and classification is 900-1350 r / min; The particle size of the modified magnesium hydroxide powder meets the following conditions: 50 14~19μm, D 97 20~25μm, D 100 The particle size of the modified magnesium hydroxide powder is 27 to 30 μm, and the activation degree of the modified magnesium hydroxide powder is ≥95%.

2. The use according to claim 1, characterized in that The mass fraction of MgO in the brucite ore is ≥58%.

3. The use according to claim 1, characterized in that The equipment used for the vibration screening is an ultrasonic vibration screen.

4. The use according to claim 1, characterized in that The equipment used for the air separation and classification is a vertical air flow classifier.

5. The use according to claim 1, characterized in that The surface modification treatment comprises mixing the pre-hydrolyzed silane coupling agent and the magnesium hydroxide obtained by air classification, wherein the particle size of the magnesium hydroxide obtained by air classification is 10 to 30 μm; the temperature of the surface modification treatment is 90° C. to 120° C., and the time of the surface modification treatment is 30 min to 60 min.

6. The use according to claim 5, characterized in that The pre-hydrolysis reaction is carried out under stirring conditions, the stirring speed of which is 10 to 30 r / min; the temperature of the pre-hydrolysis reaction is room temperature, and the time of the pre-hydrolysis reaction is 2 to 4 hours.

7. The use according to claim 5 or 6, characterized in that The silane coupling agent used to prepare the pre-hydrolyzed silane coupling agent includes at least one of γ-ureidopropyltriethoxysilane, γ-aminopropyltriethoxysilane and γ-(ethylenediamino)propyltrimethoxysilane; The mass of the silane coupling agent used to prepare the pre-hydrolyzed silane coupling agent is 0.8% to 1.5% of the mass of the magnesium hydroxide obtained by air separation and classification.

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