Preparation method of modified magnesium hydroxide and application of modified magnesium hydroxide in powder coating
By employing a series of dry ball milling and wet stirred milling processes, along with surface modification treatment, the aspect ratio and alkalinity of magnesium hydroxide were reduced, thus solving the problem of poor flowability of magnesium hydroxide in polyester/HAA powder coatings and achieving high gloss and excellent mechanical properties.
Patent Information
- Application Number
- CN202511579370.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-31
- Publication Date
- 2026-02-03
AI Technical Summary
Magnesium hydroxide is unsuitable for high-gloss coatings in polyester/HAA powder coatings due to its alkalinity and high aspect ratio, which result in poor flowability and low crosslinking density.
A dry ball milling and wet stirred milling process was adopted, combined with surface modification treatment. The aspect ratio and alkalinity of magnesium hydroxide were reduced by mechanical shearing and chemical passivation. Aminosilane and fumed silica were used to improve the surface pH. Carboxyl-terminated saturated polyester resin was added to improve compatibility.
It effectively solves the problems of poor flowability and low crosslinking density of magnesium hydroxide in powder coatings, improves the extrusion performance and film leveling of coatings, and achieves V0 flame retardant rating and excellent mechanical properties.
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Figure CN121450144A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for preparing modified magnesium hydroxide and its application in powder coatings, and is particularly suitable for outdoor powder coating scenarios with high requirements for flowability, gloss and mechanical properties. Background Technology
[0002] Magnesium hydroxide, as a highly efficient and environmentally friendly inorganic flame retardant, is increasingly widely used in the field of polymer materials due to its excellent properties, such as high heat absorption during decomposition, the ability of the generated water vapor to dilute flammable gases and cover them with flame retardant, and the absence of toxic or harmful gases.
[0003] Powder coatings, due to their solvent-free, environmentally friendly, and high-efficiency characteristics, have become an important development direction in the coatings industry. Among them, the curing system of polyester resin combined with hydroxyalkylamide (HAA) is increasingly widely used in outdoor architectural aluminum profiles, doors and windows, and other fields due to its excellent outdoor weather resistance, outstanding leveling properties, no release of toxic byproducts, and relatively low curing temperature, making it one of the mainstream alternatives to the traditional TGIC system. However, this curing system requires a suitable acidic environment to catalyze the protonation of carbonyl groups, thereby promoting the nucleophilic addition reaction. Magnesium hydroxide, under the influence of water and heat, slowly releases strongly basic hydroxyl groups (OH-). - The pH value of magnesium hydroxide is typically above 10, which significantly weakens or even completely eliminates the acidic catalytic effect, leading to a sharp decrease in the formation rate of the entire cross-linking network and thus affecting the cross-linking density of the system. Simultaneously, because magnesium hydroxide has a typical plate-like structure, the high aspect ratio plate-like particles are like "micron-sized playing cards," easily undergoing mechanical interlocking and entanglement in the powder system, generating enormous internal friction. This greatly hinders the relative sliding between particles, resulting in an increased angle of repose and a sharp decrease in flowability. The resulting powder coating has low gloss and cannot be used in high-gloss systems, severely limiting its application areas.
[0004] The alkalinity of magnesium hydroxide and its high aspect ratio are key factors limiting its application in environmentally friendly polyester / HAA powder coatings. Summary of the Invention
[0005] The purpose of this invention is to provide a method for preparing modified magnesium hydroxide and its application in powder coatings, so as to solve the problems mentioned in the background art.
[0006] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution: In a first aspect, the present invention provides a method for preparing modified magnesium hydroxide, comprising the following steps: (1) Raw material pretreatment: Select brucite concentrate with magnesium oxide content >60% as raw material. After washing and drying, it is crushed by a jaw crusher and a hammer crusher in sequence to obtain brucite particles with a diameter of 10-50mm.
[0007] (2) Dry ball milling: The brucite particles from step (1) are conveyed to a single-compartment ball mill of 1.83m×4.2m through a spiral cutter. 50mm, 40mm and 30mm steel balls are used as grinding media (mass ratio 3-5:2-4:1-2, filling rate 50-60%). After grinding, magnesium hydroxide coarse powder with D50 of 8.0-10.0μm and D97 of 44-48μm is obtained by air classification.
[0008] (3) Slurry preparation: The magnesium hydroxide coarse powder from step (2) is transported into the slurry mixing tank through the pipeline and prepared into a slurry with a solid content of 55-65%. Add No. 1 grinding aid (short-chain sodium polyacrylate with a molecular weight of 3000-6000) accounting for 2-4‰ of the dry powder mass ratio, and stir at 200-400r / min for 10-20min. (4) Wet grinding: The slurry from step (3) is transported to a 3600L vertical wet stirred mill. 1.0mm and 1.8mm zirconia beads are used as grinding media (mass ratio 3-5:1, filling rate 70-80%). No. 2 grinding aid (sodium polycarboxylate with a molecular weight of 30000-70000) is added at a mass ratio of 4-6‰ of the dry powder. Grind for 30-40 minutes. The slurry is tested by a Malvern 3000-E laser particle size analyzer to obtain a slurry with D50 of 0.8-1.0μm, D97 of 2.2-2.4μm, and ≤2μm content >80%.
[0009] (5) Liquid phase wet modification: The slurry after grinding in step (4) is transported to the reactor. First, add 1# modifier (aminosilane, hydrolyzed by ethanol) at a mass ratio of 3-5‰ of the dry powder. Modify for 10-20 min at 80-90℃ and 600-800r / min. Then add 2# modifier (fumed silica, specific surface area 350-410m² / g) at a mass ratio of 2-4‰ of the dry powder. Continue modification for 10-20 min under the same conditions.
[0010] (6) Flash drying: The wet-modified slurry from step (5) is pumped into a storage tank and flash-dried (inlet 200-220℃, outlet 80-90℃). The dried material with D50 of 1.1-1.3μm, D97 of 2.5-2.7μm, and ≤2μm content >75% is obtained by testing with a Malvern 3000-E laser particle size analyzer.
[0011] (7) Dry secondary modification: The dried material from step (6) is conveyed to a high-speed mixer via a screw conveyor for secondary surface modification treatment. 3-5‰ of the powder mass of No. 3 modifier (carboxyl-terminated saturated polyester resin, acid value 29-35 mg KOH / g) is added to the front end of the screw conveyor system. Modification is carried out for 20-30 min at 110-120℃ and 800-1000 r / min.
[0012] (8) Post-processing: After the modified material from step (7) is cooled by a cold mixer, it is transported into the finished product silo through a pipeline. The speed of the cold mixer is 300-500 r / min, the cold mixing time is 3-5 min, and finally it is sieved through a 120 mesh and tested to obtain the modified magnesium hydroxide finished product.
[0013] Furthermore, the brucite ore is a concentrate with a magnesium oxide content of ≥60%, and the magnesium hydroxide produced from high-purity brucite ore has a better flame retardant effect when used downstream.
[0014] Furthermore, the ball mill has a media filling rate of 50-60%, and the grinding media is a mixture of steel balls of different sizes with a mixing ratio of 50mm:40mm:30mm=3-5:2-4:1-2. The impact force of the grinding media converted from gravitational potential energy is used to break the magnesium hydroxide particles, thereby destroying the flake structure of magnesium hydroxide to a certain extent.
[0015] Furthermore, the slurry has a solid content of 55-65%. If the slurry concentration is too high, it will result in poor fluidity and reduced grinding efficiency. If the concentration is too low, the probability of particle collision will be low, which will also affect the grinding efficiency.
[0016] Furthermore, the No. 1 grinding aid is a short-chain sodium polyacrylate with a molecular weight of 3000-6000, which mainly reduces and prevents agglomeration through electrostatic stabilization and a certain steric hindrance effect.
[0017] The No. 2 grinding aid is a high side chain density sodium polycarboxylate with a molecular weight of 30,000-70,000. Its long side chains extend into the water to form a deep hydration layer, providing strong stereostrate stability and preventing magnesium hydroxide particles from agglomerating.
[0018] Furthermore, the grinding media in the stirred mill has a specific gravity of 6.0 g / cm³. 3 The zirconia beads have a medium filling rate of 70-80%, and the ratio of zirconia beads of different sizes is 1.0mm:1.8mm=3-5:1. The narrow gaps between the small zirconia beads generate extremely strong hydraulic shear, which can effectively peel off the layers of the sheet structure, thereby reducing the aspect ratio of magnesium hydroxide.
[0019] Furthermore, the No. 1 modifier is one or a combination of two of N-2-aminoethyl-3-aminopropyltrimethoxysilane and bis(3-trimethoxysilylpropyl)amine. Before addition, it is hydrolyzed with ethanol at a ratio of 1:3 for 15 minutes and then added to the reaction vessel. The amino group on the coupling agent is strongly adsorbed by the magnesium ions or hydroxyl groups on the surface of magnesium hydroxide through coordination bonds, hydrogen bonds or ionic bonds.
[0020] Furthermore, the No. 2 modifier is fumed silica with a specific surface area of 350-410 m² / g and a pH value of 3.7-4.5. Through the dehydration condensation between the silanol on the coupling agent and the silanol (-Si-OH) on the surface of the fumed silica, a strong Si-O-Si covalent bond is formed, which grafts the inert silica onto the surface of magnesium hydroxide and improves its surface acidity and alkalinity.
[0021] Furthermore, the No. 3 modifier is a carboxyl-terminated saturated polyester resin with an acid value of 29-35 mgKOH / g, a viscosity of 3500-5500 mPa.s / 200℃, and a softening point of 100-110℃.
[0022] Secondly, according to the first aspect above, a modified magnesium hydroxide is also provided for use in powder coatings. The amount of modified magnesium hydroxide added to the powder coating is 38-40 wt%. After application, the powder coating has excellent extrusion performance, film leveling reaches level 6, impact resistance ±50 kg·cm, adhesion level 0, and flame retardancy level V0.
[0023] The present invention has the following beneficial effects: (1) The modified magnesium hydroxide produced by this invention adopts a dry ball milling + wet stirred milling series grinding process. The mechanical impact grinding destroys the flake structure of magnesium hydroxide to a certain extent. The narrow gap between the small-sized zirconia beads generates extremely strong hydraulic shear, which can effectively peel off the flake structure layer, thereby reducing the aspect ratio of magnesium hydroxide. At the same time, through wet and dry surface modification and passivation processes, the alkalinity of the magnesium hydroxide surface is shielded, and its pH drops from the traditional 10-10.5 to 7.0-7.5, effectively solving the defects of poor flowability and low crosslinking density of magnesium hydroxide in polyester / HAA powder coating system.
[0024] (2) In this invention, aminosilane is used as a molecular bridge to graft fumed silica onto the surface of magnesium hydroxide through amino and silanol groups. The acidity of fumed silica is used to improve the alkalinity of the magnesium hydroxide surface, forming a partial physical shielding effect on the magnesium hydroxide surface. At the same time, a small amount of carboxyl-terminated saturated polyester resin with an acid value of 29-35 mgKOH / g, a viscosity of 3500-5500 mPa.s / 200℃, and a softening point of 100-110℃ is used as a physical shield and chemical barrier to further improve the surface alkalinity of magnesium hydroxide and its compatibility with downstream resins, which also indirectly improves the material flowability.
[0025] (3) This invention effectively regulates the morphology of magnesium hydroxide by using a series grinding process and surface modification and passivation technology, reduces its aspect ratio, shields its alkaline surface, and solves the defects of traditional magnesium hydroxide such as poor fluidity and affecting the crosslinking density of the paint film when it is applied to powder coatings.
[0026] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description
[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0028] Figure 1 This is a schematic diagram of the process flow of the present invention. Detailed Implementation
[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments and examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0030] Please see Figure 1 As shown, this invention relates to a method for preparing modified magnesium hydroxide and its application in powder coatings.
[0031] Implementation Plan A method for preparing modified magnesium hydroxide includes the following steps: (1) Raw material pretreatment: Select brucite concentrate with magnesium oxide content >60% as raw material. After washing and drying, it is crushed by jaw crusher and hammer crusher in sequence to obtain brucite particles with a diameter of 10-50mm. Among them, the brucite ore is concentrate with magnesium oxide content ≥60%. Magnesium hydroxide produced from high-purity brucite ore has a better flame retardant effect when used in downstream applications.
[0032] (2) Dry ball milling: The brucite particles from step (1) are conveyed to a single-compartment ball mill of 1.83m×4.2m through a spiral cutter. 50mm, 40mm and 30mm steel balls are used as grinding media (mass ratio 3-5:2-4:1-2, filling rate 50-60%). After grinding, the powder is obtained by air classification to obtain coarse magnesium hydroxide powder with D50 of 8.0-10.0μm and D97 of 44-48μm. The media filling rate of the ball mill is 50-60%. The grinding media is a compound of steel balls of different sizes. The compound ratio is 50mm:40mm:30mm=3-5:2-4:1-2. The impact force of the gravitational potential energy conversion of the grinding media is used to break the magnesium hydroxide particles, which to a certain extent destroys the plate-like structure of magnesium hydroxide.
[0033] (3) Slurry preparation: The magnesium hydroxide coarse powder from step (2) is transported into the slurry mixing tank through the pipeline and prepared into a slurry with a solid content of 55-65%. Add No. 1 grinding aid (short-chain sodium polyacrylate with a molecular weight of 3000-6000) at a mass ratio of 2-4‰ of the dry powder and stir at 200-400r / min for 10-20min. The solid content of the slurry is 55-65%. If the slurry concentration is too high, the fluidity will be poor and the grinding efficiency will decrease. If the concentration is too low, the probability of collision between particles will be low, which will also affect the grinding efficiency. In addition, No. 1 grinding aid is short-chain sodium polyacrylate with a molecular weight of 3000-6000. It mainly reduces agglomeration and prevents agglomeration through electrostatic stability and a certain steric hindrance effect.
[0034] (4) Wet grinding: The slurry from step (3) is transported to a 3600L vertical wet stirred mill. 1.0mm and 1.8mm zirconia beads are used as grinding media (mass ratio 3-5:1, filling rate 70-80%). No. 2 grinding aid (sodium polycarboxylate with a molecular weight of 30000-70000) is added at a mass ratio of 4-6‰ of the dry powder. Grind for 30-40 minutes. The slurry is tested by a Malvern 3000-E laser particle size analyzer to obtain a slurry with D50 of 0.8-1.0μm, D97 of 2.2-2.4μm, and ≤2μm content >80%. Among them, No. 2 grinding aid is sodium polycarboxylate with a molecular weight of 30000-70000. Its long side chains extend into the water to form a deep hydration layer, providing a strong three-dimensional stabilizing effect and preventing magnesium hydroxide particles from agglomerating. In addition, the grinding media of the stirred mill has a specific gravity of 6.0 g / cm³. 3 The zirconia beads have a medium filling rate of 70-80%, and the ratio of zirconia beads of different sizes is 1.0mm:1.8mm=3-5:1. The narrow gaps between the small zirconia beads generate extremely strong hydraulic shear, which can effectively peel off the layers of the sheet structure, thereby reducing the aspect ratio of magnesium hydroxide.
[0035] (5) Liquid-phase wet modification: The slurry after grinding in step (4) is transported to the reactor. First, add 3-5‰ of the dry powder mass of No. 1 modifier (aminosilane, hydrolyzed by ethanol), and modify it for 10-20 min at 80-90℃ and 600-800 r / min. Then add 2-4‰ of the dry powder mass of No. 2 modifier (fumed silica, specific surface area 350-410 m² / g), and continue modification for 10-20 min under the same conditions. Among them, No. 1 modifier is one of N-2-aminoethyl-3-aminopropyltrimethoxysilane and bis(3-trimethoxysilylpropyl)amine. One or two types are combined. Before adding, the modifier is hydrolyzed with ethanol at a ratio of 1:3 for 15 minutes and then added to the reaction vessel. The amino groups on the coupling agent are strongly adsorbed by the magnesium ions or hydroxyl groups on the surface of magnesium hydroxide through coordination bonds, hydrogen bonds or ionic bonds. Modifier #2 is fumed silica with a specific surface area of 350-410 m² / g and a pH of 3.7-4.5. The silanols on the coupling agent undergo dehydration condensation with the silanols (-Si-OH) on the surface of fumed silica to form strong Si-O-Si covalent bonds, grafting inert silica onto the surface of magnesium hydroxide and improving its surface pH.
[0036] (6) Flash drying: The wet-modified slurry from step (5) is pumped into a storage tank and flash-dried (inlet 200-220℃, outlet 80-90℃). The dried material with D50 of 1.1-1.3μm, D97 of 2.5-2.7μm, and ≤2μm content >75% is obtained by testing with a Malvern 3000-E laser particle size analyzer.
[0037] (7) Dry secondary modification: The dried material from step (6) is conveyed to a high-speed mixer via a screw conveyor for secondary surface modification treatment. 3-5‰ of the powder mass of No. 3 modifier (carboxyl-terminated saturated polyester resin, acid value 29-35 mg KOH / g) is added to the front end of the screw conveyor system. Modification is carried out at 110-120℃ and 800-1000 r / min for 20-30 min. No. 3 modifier is a carboxyl-terminated saturated polyester resin with an acid value of 29-35 mg KOH / g, a viscosity of 3500-5500 mPa.s / 200℃, and a softening point of 100-110℃.
[0038] (8) Post-processing: After the modified material from step (7) is cooled by a cold mixer, it is transported into the finished product silo through a pipeline. The speed of the cold mixer is 300-500 r / min, the cold mixing time is 3-5 min, and finally it is sieved through a 120 mesh and tested to obtain the modified magnesium hydroxide finished product.
[0039] Secondly, according to the first aspect mentioned above, a modified magnesium hydroxide is also provided for use in powder coatings. The amount of modified magnesium hydroxide added to the powder coating is 38-40 wt%. After application, the powder coating has excellent extrusion performance, film leveling reaches level 6, impact resistance ±50 kg·cm, adhesion level 0, and flame retardancy level V0.
[0040] Based on the above implementation scheme, the present invention also provides the following embodiments for further detailed description.
[0041] Example 1 Using brucite concentrate with a magnesium oxide content >60% as raw material, after washing, drying and crushing by jaw crusher and hammer crusher, brucite particles with a diameter of 10-50mm are obtained. The material is conveyed by a rotary cutter into a 1.83m*4.2m single-compartment ball mill for primary grinding. After air classification, coarse magnesium hydroxide powder with D50 of 9.27um and D97 of 47.66um is obtained. The coarse powder was transported through a pipeline into the No. 1 slurry mixing tank to prepare a slurry with a solid content of 55%. Sokalan PA30 dispersant, which accounts for 2‰ of the dry powder mass, was added. The mixing tank speed was 200 r / min and the mixing time was 10min. The slurry was pumped into a 3600L vertical wet stirred mill for wet grinding. The grinding media was zirconia beads with a media filling rate of 55% and a media ratio of 1.0mm:1.8mm = 3:1. Dispex® Ultra PX 4540 dispersant, accounting for 4‰ of the dry powder mass, was added to the top of the stirred mill. The grinding time was 30 minutes. The slurry was tested with a Malvern 3000-E laser particle size analyzer and found that the D50 was 0.98µm, the D97 was 2.36µm, and the content of ≤2µm was 81.2%. After grinding, the slurry is pumped into the reactor. Modifier No. 1 (N-2-aminoethyl-3-aminopropyltrimethoxysilane) at a mass ratio of 3‰ of the dry powder is added at the reactor inlet for liquid-phase wet modification. The reactor speed is 600 r / min, the reactor temperature is 80℃, and the modification time is 10 min. Continue adding 2‰ of the dry powder mass of No. 2 fumed silica (A380), and modify for 10 minutes under the above conditions. The wet-modified slurry is pumped into a storage tank, flash-dried, collected, and stored in a silo for later use. The particle size distribution is measured by a Malvern 3000-E laser particle size analyzer, with D50 of 1.28 μm, D97 of 2.64 μm, and ≤2 μm content of 75.36%. The material in the silo is conveyed into the high-speed mixer via a screw conveyor for secondary surface modification treatment. Modifier No. 3 (SJ5801 polyester resin) with a mass ratio of 3‰ of the powder is added at the front end of the screw conveyor system. The high-speed mixer speed is 800 r / min, the heat transfer oil temperature is 110℃, and the modification time is 20 min. After being cooled by a cold mixer, the material is transported into the finished product silo via pipeline. The cold mixer speed is 300 r / min, the cold mixing time is 3 (3-5) min, and finally it is sieved through a 120 mesh sieve for testing and packaging.
[0042] Example 2 Using brucite concentrate with a magnesium oxide content >60% as raw material, after washing, drying and crushing by jaw crusher and hammer crusher, brucite particles with a diameter of 10-50mm are obtained. The material is conveyed by a rotary cutter into a 1.83m*4.2m single-compartment ball mill for primary grinding. After air classification, coarse magnesium hydroxide powder with D50 of 8.99um and D97 of 46.01um is obtained. The coarse powder was transported through a pipeline into the No. 1 slurry mixing tank to prepare a slurry with a solid content of 60%. Sokalan PA30 dispersant, which accounts for 3‰ of the dry powder mass, was added. The mixing tank speed was 300 r / min and the mixing time was 15min. The slurry was pumped into a 3600L vertical wet stirred mill for wet grinding. The grinding media was zirconia beads with a media filling rate of 60% and a media ratio of 1.0mm:1.8mm = 4:1. Dispex® Ultra PX 4540 dispersant, accounting for 5‰ of the dry powder mass, was added to the top of the stirred mill. The grinding time was 35 minutes. The slurry was tested with a Malvern 3000-E laser particle size analyzer and found that the D50 was 0.91µm, the D97 was 2.30µm, and the content of ≤2µm was 83.4%. After grinding, the slurry is pumped into the reactor. Modifier No. 1 (bis(3-trimethoxysilylpropyl)amine) at a mass ratio of 4‰ of the dry powder is added at the reactor inlet for liquid-phase wet modification. The reactor rotation speed is 700 r / min, the reactor temperature is 85℃, and the modification time is 15 min. Continue adding No. 2 fumed silica (A380) at a dry powder mass ratio of 3‰, and modify for 15 minutes under the above conditions. The wet-modified slurry is pumped into a storage tank, flash-dried, collected, and then stored in a silo for later use. The particle size distribution is measured by a Malvern 3000-E laser particle size analyzer, with D50 of 1.21 μm, D97 of 2.56 μm, and ≤2 μm content of 77.87%. The material in the silo is conveyed into the high-speed mixer via a screw conveyor for secondary surface modification treatment. Modifier No. 3 (SJ5801 polyester resin) with a mass ratio of 4‰ of the powder is added at the front end of the screw conveyor system. The high-speed mixer speed is 900 r / min, the heat transfer oil temperature is 115℃, and the modification time is 25 min. After being cooled by a cold mixer, the material is transported into the finished product silo via pipeline. The cold mixer speed is 400 r / min, the cold mixing time is 4 (3-5) min, and finally it is sieved through a 120 mesh sieve for testing and packaging.
[0043] Example 3 Using brucite concentrate with a magnesium oxide content >60% as raw material, after washing, drying and crushing by jaw crusher and hammer crusher, brucite particles with a diameter of 10-50mm are obtained. The material is conveyed by a rotary cutter into a 1.83m*4.2m single-compartment ball mill for primary grinding. After air classification, coarse magnesium hydroxide powder with D50 of 8.56um and D97 of 44.87um is obtained. The coarse powder was transported through a pipeline into the No. 1 slurry mixing tank to prepare a slurry with a solid content of 65%. Sokalan PA30 dispersant, which accounted for 4‰ of the dry powder mass, was added. The mixing tank was rotated at 400 r / min and the mixing time was 20min. The slurry was pumped into a 3600L vertical wet stirred mill for wet grinding. The grinding media was zirconia beads with a media filling rate of 65% and a media ratio of 1.0mm:1.8mm = 5:1. Dispex® Ultra PX 4540 dispersant, accounting for 6‰ of the dry powder mass, was added to the top of the stirred mill. The grinding time was 40 minutes. The slurry was tested with a Malvern 3000-E laser particle size analyzer and found that the D50 was 0.84µm, the D97 was 2.23µm, and the content of ≤2µm was 89.5%. After grinding, the slurry is pumped into the reactor. Modifier No. 1 (N-2-aminoethyl-3-aminopropyltrimethoxysilane: bis(3-trimethoxysilylpropyl)amine = 1:1) is added at 5‰ of the dry powder mass ratio at the reactor inlet for liquid-phase wet modification. The reactor rotation speed is 800 r / min, the reactor temperature is 90℃, and the modification time is 20 min. Continue adding No. 2 fumed silica (A380) at a dry powder mass ratio of 4‰, and modify for 20 minutes under the above conditions. The wet-modified slurry is pumped into a storage tank, flash-dried, collected, and then stored in a silo for later use. The particle size distribution is measured by a Malvern 3000-E laser particle size analyzer, with D50 of 1.18 μm, D97 of 2.52 μm, and ≤2 μm content of 82.21%. The material in the silo is conveyed into the high mixer via a screw conveyor for secondary surface modification treatment. 3# modifier (SJ5801 polyester resin) with a mass ratio of 5‰ of the powder is added at the front end of the screw conveyor system. The high mixer speed is 1000 r / min, the heat transfer oil temperature is 120℃, and the modification time is 30 min. After being cooled by a cold mixer, the material is transported into the finished product silo via pipeline. The cold mixer operates at a speed of 500 r / min and the cold mixing time is 5 minutes. Finally, the material is sieved through a 120-mesh sieve for testing and packaging.
[0044] Example 4 In this embodiment, the modified magnesium hydroxide prepared in Examples 1-3 above and the modified magnesium hydroxide products produced by conventional processes were tested for relevant indicators according to HG / T 3607-2007. The relevant indicators are as follows:
[0045] As can be seen from the table above, compared with traditional modified magnesium hydroxide, the pH value and aspect ratio of the products produced using the patented technology route of this invention in Examples 1-3 are significantly lower than those of traditional modified magnesium hydroxide products. At the same time, the particle size, oil absorption, moisture content and other indicators are all better than those of traditional modified magnesium hydroxide.
[0046] Example 5 This embodiment applies the modified magnesium hydroxide prepared in Examples 1-3 above to a polyester / HAA flame-retardant powder coating system, compares it with traditional modified magnesium hydroxide, and tests it according to relevant standards.
[0047] The formula for interior wall latex paint is:
[0048] The test results are shown in the table below.
[0049] As can be seen from the table above, when the modified magnesium hydroxide products produced using the technology of this invention in Examples 1, 2, and 3 are applied to polyester / HAA powder coatings, their extrusion performance and leveling properties are significantly better than those of traditional modified magnesium hydroxide products. At the same time, their mechanical properties such as impact resistance and adhesion are also significantly better than those of conventional products. When applied to this system, they can effectively improve the leveling properties of the coating and increase the crosslinking density of the coating film.
[0050] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.
Claims
1. A method for preparing modified magnesium hydroxide, characterized in that, Includes the following steps: (1) Raw material pretreatment: Select brucite concentrate with magnesium oxide content >60% as raw material. After washing and drying, it is crushed by a jaw crusher and a hammer crusher in sequence to obtain brucite particles with a diameter of 10-50mm. (2) Dry ball milling: The brucite particles from step (1) are conveyed to a single-compartment ball mill of 1.83m×4.2m through a spiral cutter. 50mm, 40mm and 30mm steel balls are used as grinding media (mass ratio 3-5:2-4:1-2, filling rate 50-60%). After grinding, magnesium hydroxide coarse powder with D50 of 8.0-10.0μm and D97 of 44-48μm is obtained by air classification. (3) Slurry preparation: The magnesium hydroxide coarse powder from step (2) is transported into the slurry mixing tank through the pipeline and prepared into a slurry with a solid content of 55-65%. Add No. 1 grinding aid (short-chain sodium polyacrylate with a molecular weight of 3000-6000) accounting for 2-4‰ of the dry powder mass ratio, and stir at 200-400r / min for 10-20min. (4) Wet grinding: The slurry from step (3) is transported to a 3600L vertical wet stirred mill. 1.0mm and 1.8mm zirconia beads are used as grinding media (mass ratio 3-5:1, filling rate 70-80%). No. 2 grinding aid (sodium polycarboxylate with a molecular weight of 30000-70000) is added at a mass ratio of 4-6‰ of the dry powder. Grind for 30-40 minutes. The slurry is tested by a Malvern 3000-E laser particle size analyzer to obtain a slurry with D50 of 0.8-1.0μm, D97 of 2.2-2.4μm, and ≤2μm content >80%. (5) Liquid phase wet modification: The slurry after grinding in step (4) is transported to the reactor. First, add 1# modifier (aminosilane, hydrolyzed by ethanol) at a mass ratio of 3-5‰ of the dry powder. Modify for 10-20 min at 80-90℃ and 600-800r / min. Then add 2# modifier (fumed silica, specific surface area 350-410m² / g) at a mass ratio of 2-4‰ of the dry powder. Continue modification for 10-20 min under the same conditions. (6) Flash drying: The slurry modified by wet method in step (5) is pumped into a slurry storage tank and flash dried (inlet 200-220℃, outlet 80-90℃). The dried material with D50 of 1.1-1.3μm, D97 of 2.5-2.7μm and ≤2μm content >75% is obtained by testing with a Malvern 3000-E laser particle size analyzer. (7) Dry secondary modification: The dried material from step (6) is conveyed to a high-speed mixer via a screw conveyor for secondary surface modification treatment. 3-5‰ of the powder mass of No. 3 modifier (carboxyl-terminated saturated polyester resin, acid value 29-35 mg KOH / g) is added to the front end of the screw conveyor system. Modification is carried out for 20-30 min at 110-120℃ and 800-1000 r / min. (8) Post-processing: After the modified material from step (7) is cooled by a cold mixer, it is transported into the finished product silo through a pipeline. The speed of the cold mixer is 300-500 r / min, the cold mixing time is 3-5 min, and finally it is sieved through a 120 mesh and tested to obtain the modified magnesium hydroxide finished product.
2. The method for preparing modified magnesium hydroxide according to claim 1, characterized in that, The brucite ore is a concentrate with a magnesium oxide content of ≥60%. Magnesium hydroxide produced from high-purity brucite ore has a better flame retardant effect when used downstream.
3. The method for preparing modified magnesium hydroxide according to claim 1, characterized in that, The ball mill has a media filling rate of 50-60%, and the grinding media is a mixture of steel balls of different sizes with a mixing ratio of 50mm:40mm:30mm=3-5:2-4:1-2. The impact force of the grinding media converted from gravitational potential energy is used to break the magnesium hydroxide particles, thereby destroying the flake structure of magnesium hydroxide to a certain extent.
4. The method for preparing modified magnesium hydroxide according to claim 1, characterized in that, The slurry has a solid content of 55-65%. If the slurry concentration is too high, it will result in poor fluidity and reduced grinding efficiency. If the concentration is too low, the probability of particle collision will be low, which will also affect the grinding efficiency.
5. The method for preparing modified magnesium hydroxide according to claim 1, characterized in that, The No. 1 grinding aid is a short-chain sodium polyacrylate with a molecular weight of 3000-6000, which mainly reduces and prevents agglomeration through electrostatic stabilization and a certain steric hindrance effect. The No. 2 grinding aid is a high side chain density sodium polycarboxylate with a molecular weight of 30,000-70,000. Its long side chains extend into the water to form a deep hydration layer, providing strong stereostrate stability and preventing magnesium hydroxide particles from agglomerating.
6. The method for preparing modified magnesium hydroxide according to claim 1, characterized in that, The grinding media in the stirred mill has a specific gravity of 6.0 g / cm³. 3 The zirconia beads have a medium filling rate of 70-80%, and the ratio of zirconia beads of different sizes is 1.0mm:1.8mm=3-5:
1. The narrow gaps between the small zirconia beads generate extremely strong hydraulic shear, which can effectively peel off the layers of the sheet structure, thereby reducing the aspect ratio of magnesium hydroxide.
7. The method for preparing modified magnesium hydroxide according to claim 1, characterized in that, The No. 1 modifier is one or a combination of two of N-2-aminoethyl-3-aminopropyltrimethoxysilane and bis(3-trimethoxysilylpropyl)amine. Before addition, it is hydrolyzed with ethanol at a ratio of 1:3 for 15 minutes and then added to the reaction vessel. The amino group on the coupling agent is strongly adsorbed by the magnesium ions or hydroxyl groups on the surface of magnesium hydroxide through coordination bonds, hydrogen bonds or ionic bonds.
8. The method for preparing modified magnesium hydroxide according to claim 1, characterized in that, The No. 2 modifier has a specific surface area of 350-410 m². 2 / g of fumed silica with a pH of 3.7-4.5 is grafted onto the surface of magnesium hydroxide by dehydration condensation between silanol on the coupling agent and silanol (-Si-OH) on the surface of fumed silica to form strong Si-O-Si covalent bonds, thereby improving the pH of the surface of inert silica.
9. The method for preparing modified magnesium hydroxide according to claim 1, characterized in that, The No. 3 modifier is a carboxyl-terminated saturated polyester resin with an acid value of 29-35 mgKOH / g, a viscosity of 3500-5500 mPa.s / 200℃, and a softening point of 100-110℃.
10. An application of modified magnesium hydroxide in powder coatings, wherein the modified magnesium hydroxide is prepared using the method described in claims 1-9 above, and the modified magnesium hydroxide product prepared is used in powder coatings, characterized in that... The modified magnesium hydroxide is added to the powder coating at a rate of 38-40 wt%. After application, the powder coating exhibits excellent extrusion performance, a film leveling property of grade 6, an impact resistance of ±50 kg·cm, an adhesion grade of grade 0, and a flame retardancy grade of V0.