Preparation method of flaky magnesium hydroxide flame retardant
By employing precipitation synthesis and epoxy coating methods, the problems of harsh preparation conditions and insufficient flame retardant properties of nanoscale flake magnesium hydroxide were solved, enabling the industrial-scale preparation of nanoscale flake magnesium hydroxide and improving its flame retardant properties in polymer materials.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHANDONG AIKE POLYMER MATERIAL CO LTD
- Filing Date
- 2026-04-14
- Publication Date
- 2026-05-12
AI Technical Summary
Existing methods for preparing nanoscale sheet magnesium hydroxide are subject to harsh conditions, making industrialization difficult and resulting in insufficient flame retardant properties, which limits its application in polymer materials.
By employing a precipitation method and epoxy coating, and utilizing pH buffers, morphology control agents, and dispersants to control the pH value and morphology of the reaction system, combined with organic coating to improve dispersibility, nanoscale flake magnesium hydroxide with controllable particle size and morphology was prepared.
Under simple and mild process conditions, the industrial production of nano-scale flake magnesium hydroxide was achieved, which improved its flame retardant properties in EVA, increased the limiting oxygen index to over 31, and achieved a UL94 vertical flammability rating of V-1.
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Figure CN122011806A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for preparing flake magnesium hydroxide flame retardant, belonging to the field of inorganic material preparation technology. Background Technology
[0002] Magnesium hydroxide is a white, odorless solid that is almost insoluble in water. As a novel inorganic and environmentally friendly functional material, it has shown application potential in the preparation of flame retardants, water treatment agents, pharmaceutical antacids, and the preservation of historical relics. When used as a flame retardant, the particle size of magnesium hydroxide is the most important influencing factor, affecting the mechanical and flame-retardant properties of polymer materials. Compared to common micron-sized magnesium hydroxide, nano-sized magnesium hydroxide has many significant advantages: the nanoscale size and high specific surface area of nano-sized magnesium hydroxide can increase its contact area with flame-retardant materials, improving the flame-retardant effect. In particular, nano-sized flake magnesium hydroxide, due to its higher specific surface area, can achieve the same or even better flame-retardant effect with a lower addition amount, thereby reducing the amount of material used, helping to reduce production costs and resource consumption. Furthermore, the flake morphology of magnesium hydroxide is relatively easier to disperse, resulting in less loss of mechanical properties and thus reducing the damage to the mechanical properties of the matrix material caused by the addition of magnesium hydroxide flame retardant. In summary, nanoscale flake magnesium hydroxide has a smaller particle size, superior morphology, and lower filler content compared to micron-sized magnesium hydroxide. It also exhibits the volume effect, surface effect, and quantum size effect of nanomaterials, demonstrating significant effectiveness in enhancing the properties of polymer materials. Therefore, nanoscale flake magnesium hydroxide flame retardants have broad application prospects, and their preparation and modification technologies have received considerable attention and extensive research.
[0003] Chinese patent CN116284996A discloses a method for preparing hexagonal flake-shaped magnesium hydroxide flame retardant, comprising the following steps: a precipitant and a magnesium chloride solution are simultaneously added to a vertical ultrasonic tubular reactor for precipitation reaction, resulting in magnesium hydroxide precipitate. This precipitate is then reacted with a hydrothermal modifier in a microwave-stirred reactor to obtain the magnesium hydroxide flame retardant. The ultrasonic tubular reactor is a bottom-in, top-out type, with a molar ratio of precipitant (hydroxyl ions) to magnesium chloride solution (magnesium ions) of 2:1. The linear velocity at the tip of the stirring blade in the microwave-stirred reactor is 0.5~1.5 m / s, and the hydrothermal reaction time is 30~120 min. While the hexagonal flake-shaped magnesium hydroxide flame retardant obtained by this patent has good particle size and morphology, it must be obtained through a hydrothermal process. The hydrothermal synthesis equipment is complex and expensive, and the conditions are relatively harsh, making industrial implementation currently difficult.
[0004] Chinese patent CN120057960A discloses a method for synthesizing hexagonal flake magnesium hydroxide and its flame-retardant application, including: Step 1, dissolving a mineralizing agent, a crystal form control agent, and magnesium chloride in water in a certain proportion; Step 2, placing a certain amount of the mixed solution into a high-pressure reactor for hydrothermal reaction; Step 3, after the reaction is completed, removing the cooled solution from the high-pressure reactor and filtering to separate the white product; Step 4, drying the sample and grinding it to obtain pure magnesium hydroxide powder. This patent still relies on hydrothermal reaction to obtain hexagonal flake magnesium hydroxide with good particle size and morphology, which has limitations in industrial implementation. Moreover, according to the flame-retardant performance test data disclosed in this patent, when the addition amount of EVA reaches 50wt%, the oxygen index only reaches about 30, and the flame-retardant level can only reach UL-94 V-2 level.
[0005] As can be seen above, the preparation of nanoscale flake magnesium hydroxide still faces prominent problems such as harsh synthesis conditions, difficulty in industrialization, and poor flame retardant performance. Therefore, developing a method for preparing a highly efficient flame retardant nanoscale flake magnesium hydroxide that is easy to scale up industrially is of great significance for improving the flame retardant performance of polymer materials. Summary of the Invention
[0006] To address the shortcomings of the existing technology, this invention provides a method for preparing flake magnesium hydroxide flame retardant, achieving the following objective: to develop a method for preparing a nanoscale flake magnesium hydroxide high-efficiency flame retardant that is easy to scale up industrially, and to prepare nanoscale flake magnesium hydroxide with controllable particle size and morphology and excellent flame retardant properties.
[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: A method for preparing a flake-shaped magnesium hydroxide flame retardant, the method comprising two steps: precipitation synthesis and epoxy coating; The following are further improvements to the above technical solution: Step 1: Precipitation synthesis Magnesium salt, pH buffer, morphology control agent, dispersant, and deionized water are placed in a reaction vessel and stirred until completely dissolved. The temperature is then raised to the reaction temperature, and ammonia water is added dropwise under constant temperature and stirring. The dropping rate is controlled to stabilize the pH value of the reaction system at 9.8~10.3. After the addition is complete, stirring is continued until the reaction is complete. The product is then discharged, filtered, washed, and dried to obtain the initial product of flake magnesium hydroxide flame retardant. The magnesium salt is one or a mixture of any two or more of magnesium nitrate, magnesium chloride, and magnesium sulfate in any mass ratio. The pH buffer is a mixture of 2,4,6-tris(aminohexanoic acid)-1,3,5-triazine and triethanolamine borate; The mass ratio of 2,4,6-tris(aminohexanoic acid)-1,3,5-triazine to triethanolamine borate is 13~37:45; The morphology control agent is one or a mixture of two of succinic dihydrazide and 2,3-dihydroxysuccinic dihydrazide in any mass ratio. The dispersant is one or a mixture of two of sodium polymethacrylate and ammonium polymethacrylate in any mass ratio; The mass concentration of the ammonia solution is 6-15 wt%. The mass ratio of the magnesium salt, pH buffer, morphology control agent, dispersant, deionized water, and ammonia is 35~115:3~11:2~10:1~6:290~880:110~540; The constant temperature stirring has a stirring speed of 500~1600 rpm; The reaction temperature is 30~65℃; Continue stirring until the reaction is complete, with a stirring time of 2 to 3.5 hours; The washing process involves washing with deionized water until the pH of the washing solution reaches 7.2-7.8. The drying process involves drying at 80-110°C for 12-25 hours.
[0008] Step 2: Epoxy Coating E20 epoxy resin, methyl methacrylate resin, and ethylene glycol monobutyl ether were placed in a dispersion reactor and stirred until completely dissolved. Then, the initial product of flake magnesium hydroxide flame retardant was added and strongly dispersed evenly. The temperature was raised to the reaction temperature, and diethylenetriamine was added under low-speed dispersion. After the curing reaction was complete, the product was discharged at room temperature. After filtration, washing, and drying, the flake magnesium hydroxide flame retardant was obtained. The mass ratio of E20 epoxy resin, methyl methacrylate resin, ethylene glycol monobutyl ether, flake magnesium hydroxide flame retardant primary product, and diethylenetriamine is 20~80:1~10:500~1200:150~330:2~11; The strong dispersion is uniform, with a dispersion rate of 8000~10000 rpm and a dispersion time of 5~9 hours; The reaction temperature is 40~75℃; The low-speed dispersion has a dispersion rate of 1000~2000 rpm; The curing reaction is complete, and the curing reaction time is 4 to 9 hours; The washing process involves washing with anhydrous ethanol 3 to 5 times, with the amount of anhydrous ethanol used each time being equal to the mass of the wet solid being washed. The drying process involves drying at 80-100°C for 6-13 hours.
[0009] Compared with the prior art, the present invention achieves the following beneficial effects: 1. This invention utilizes the precipitation method and designs a one-way drop precipitation reaction system to prepare nanoscale flake magnesium hydroxide with controllable particle size and morphology and excellent flame retardant properties under relatively simple, mild and easy-to-control process conditions. This has obvious advantages over the harsh reaction conditions of hydrothermal synthesis and is easy to scale up for industrial application. 2. This invention uses a mixture of 2,4,6-tris(aminohexanoyl)-1,3,5-triazine and triethanolamine borate to buffer pH fluctuations in the reaction system. The triethanolamine moiety of the triethanolamine borate is weakly basic, and the boron atom in the borate moiety has an empty p orbital, exhibiting Lewis acid properties. The triethanolamine borate formed by the combination of these two moieties can partially dissociate or undergo coordination equilibrium in water, forming a weak acid-weak base pair, which can generally stabilize the pH of the reaction system at 8.5~10. Within a pH range of 5, excessive fluctuations in the pH of the reaction system are suppressed. Furthermore, 2,4,6-tris(aminohexanoic acid)-1,3,5-triazine is a weakly acidic ternary organic carboxylic acid, readily soluble in alkaline environments with a pH greater than 8.5, forming weak acid-strong base salts or weak acid-weak base salts. Both types of salts can act as acid-base buffers within a certain pH range. Therefore, the combination of 2,4,6-tris(aminohexanoic acid)-1,3,5-triazine and triethanolamine borate is highly beneficial for stabilizing pH fluctuations in the precipitation reaction system. 2,4,6-Tris(aminohexanoic acid)-1,3,5-triazine contains a carbonyl oxygen atom in the form of a carboxyl group. This chemical structure has a very strong chelating effect on metal ions. Therefore, 2,4,6-tris(aminohexanoic acid)-1,3,5-triazine has a certain chelating effect on magnesium ions in the reaction system and has a certain regulatory effect on the concentration of magnesium ions in the reaction system. That is, it can affect the precipitation reaction rate by adjusting the free concentration of magnesium ions. Numerous research papers have shown that a lower pH alkaline environment and a lower concentration of reactants help to slow down the precipitation reaction rate and are more conducive to avoiding the formation of magnesium hydroxide gel. This makes the morphology and particle size of magnesium hydroxide precipitate particles more controllable. The pH buffer used in this invention is mainly used to control the fluctuation of the buffer pH value, realize a weakly alkaline environment in the reaction system, and at the same time use the chelating effect to reduce the concentration of magnesium ions in the reaction system, so as to slow down the formation rate of magnesium hydroxide precipitate particles to the maximum extent, so as to facilitate the regulatory role of other auxiliaries or reaction components. 3. The morphology control agents added in this invention, namely succinic acid dihydrazide and 2,3-dihydroxysuccinic acid dihydrazide, mainly function to control the two-dimensional planar shape of flake magnesium hydroxide, that is, to make the flake magnesium hydroxide appear as approximately hexagonal as possible. Scanning electron microscopy images show that the morphology control agents have played the above role. The reason may be that the hydrazide groups contained in these two substances, namely CONHNH2, can form particularly strong hydrogen bonds with hydroxyl groups on the surface of magnesium hydroxide. It is possible that the growth of flake magnesium hydroxide in the two-dimensional plane is somewhat restricted due to the influence of this hydrogen bond force, and this restriction causes the magnesium hydroxide flakes to tend to form hexagonal shapes. 4. The sodium polymethacrylate and ammonium polymethacrylate added to the reaction system in this invention have a good dispersing effect as dispersants. The mechanism of action is mainly to utilize the steric hindrance and charge repulsion of these two polymers to weaken the hydrogen bonding and van der Waals forces between the flake magnesium hydroxide, slow down the aggregation rate between the flake magnesium hydroxide, and thus obtain a nano-sized microparticle suspension with a dispersion degree close to that of single particles. 5. In this invention, flake magnesium hydroxide is organically coated with E20 epoxy resin and methyl methacrylate resin to promote the compatibility between magnesium hydroxide and the organic resin matrix and improve the uniformity of magnesium hydroxide dispersion in the organic resin matrix. Relevant tests using EVA to test its flame retardant performance show that magnesium hydroxide co-coated with E20 epoxy resin and methyl methacrylate resin can be easily uniformly dispersed in EVA. An addition of 40wt% can increase the limiting oxygen index of EVA to above 31 and the UL94 vertical burning rating to V-1. This fully demonstrates the high efficiency of the nano-scale flake magnesium hydroxide obtained by this invention in improving flame retardant performance. 6. The particle size distribution of the flake magnesium hydroxide flame retardant obtained by this invention, as measured by a laser particle size analyzer, is D. 10 In the range of 0.022~0.034μm, D 50 In the range of 0.591~0.608μm, D 90 When added to EVA at a concentration of 40 wt% at a depth of 1.398–1.749 μm, the limiting oxygen index of EVA increases to 31.1–32.0%, and the UL94 vertical flammability rating can reach V-1. Attached Figure Description
[0010] Figure 1 A scanning electron microscope image magnified 10,000 times of the original product of the flake magnesium hydroxide flame retardant obtained in Example 1; Figure 2 A scanning electron microscope image at 10,000x magnification of the flake magnesium hydroxide flame retardant obtained in Example 1; Figure 3A scanning electron microscope image magnified 10,000 times for the initial product of the flake magnesium hydroxide flame retardant obtained in Comparative Example 1; Figure 4 The image shown is a scanning electron microscope image magnified 10,000 times, of the initial product of the flake magnesium hydroxide flame retardant obtained in Comparative Example 2. Detailed Implementation
[0011] The preferred embodiments of the present invention are described below. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.
[0012] Example 1: A method for preparing a flake magnesium hydroxide flame retardant Step 1: Precipitation synthesis Magnesium salt, pH buffer, morphology control agent, dispersant, and deionized water are placed in a reaction vessel and stirred until completely dissolved. The temperature is then raised to the reaction temperature, and ammonia water is added dropwise under constant temperature and stirring. The dropping rate is controlled to keep the pH value of the reaction system stable at 10. After the addition is complete, stirring is continued until the reaction is complete. The product is then discharged, filtered, washed, and dried to obtain the initial product of flake magnesium hydroxide flame retardant. The magnesium salt is magnesium nitrate; The pH buffer is a mixture of 2,4,6-tris(aminohexanoic acid)-1,3,5-triazine and triethanolamine borate; The mass ratio of 2,4,6-tris(aminohexanoic acid)-1,3,5-triazine to triethanolamine borate is 29:45; The morphology control agent is succinic dihydrazide; The dispersant is sodium polymethacrylate; The mass concentration of the ammonia solution is 11 wt%. The mass ratio of the magnesium salt, pH buffer, morphology control agent, dispersant, deionized water, and ammonia is 80:7:4:2:590:440. The constant temperature stirring has a stirring rate of 1100 rpm; The reaction temperature is 55°C; Continue stirring until the reaction is complete, and the stirring reaction time is 3 hours; The washing process involves washing with deionized water until the pH of the washing solution reaches 7.5. The drying process involves drying at 100°C for 17 hours.
[0013] Step 2: Epoxy Coating E20 epoxy resin, methyl methacrylate resin, and ethylene glycol monobutyl ether were placed in a dispersion reactor and stirred until completely dissolved. Then, the initial product of flake magnesium hydroxide flame retardant was added and strongly dispersed evenly. The temperature was raised to the reaction temperature, and diethylenetriamine was added under low-speed dispersion. After the curing reaction was complete, the product was discharged at room temperature. After filtration, washing, and drying, the flake magnesium hydroxide flame retardant was obtained. The mass ratio of E20 epoxy resin, methyl methacrylate resin, ethylene glycol monobutyl ether, flake magnesium hydroxide flame retardant primary product, and diethylenetriamine is 45:6:900:260:7. The strong dispersion is uniform, with a dispersion rate of 9000 rpm and a dispersion time of 7 hours; The reaction temperature is 70°C; The low-speed dispersion has a dispersion rate of 1300 rpm; The curing reaction is complete, and the curing reaction time is 6 hours; The washing process involves washing four times with anhydrous ethanol, with the amount of anhydrous ethanol used each time being equal to the mass of the wet solid being washed. The drying process involves drying at 95°C for 11 hours.
[0014] Example 2: A method for preparing a flake-shaped magnesium hydroxide flame retardant Step 1: Precipitation synthesis Magnesium salt, pH buffer, morphology control agent, dispersant, and deionized water are placed in a reaction vessel and stirred until completely dissolved. The temperature is then raised to the reaction temperature, and ammonia water is added dropwise under constant temperature and stirring. The dropping rate is controlled to stabilize the pH value of the reaction system at 9.8. After the addition is complete, stirring is continued until the reaction is complete. The product is then discharged, filtered, washed, and dried to obtain the initial product of flake magnesium hydroxide flame retardant. The magnesium salt is magnesium chloride; The pH buffer is a mixture of 2,4,6-tris(aminohexanoic acid)-1,3,5-triazine and triethanolamine borate; The mass ratio of 2,4,6-tris(aminohexanoic acid)-1,3,5-triazine to triethanolamine borate is 13:45; The morphology control agent is 2,3-dihydroxysuccinic acid dihydrazide; The dispersant is ammonium polymethacrylate; The mass concentration of the ammonia solution is 6 wt%. The mass ratio of the magnesium salt, pH buffer, morphology control agent, dispersant, deionized water, and ammonia is 35:3:2:1:290:110. The constant temperature stirring is carried out at a stirring rate of 500 rpm. The reaction temperature is 30°C; Continue stirring until the reaction is complete; the stirring reaction time is 3.5 hours. The washing process involves washing with deionized water until the pH of the washing solution reaches 7.2. The drying process involves drying at 80°C for 25 hours.
[0015] Step 2: Epoxy Coating E20 epoxy resin, methyl methacrylate resin, and ethylene glycol monobutyl ether were placed in a dispersion reactor and stirred until completely dissolved. Then, the initial product of flake magnesium hydroxide flame retardant was added and strongly dispersed evenly. The temperature was raised to the reaction temperature, and diethylenetriamine was added under low-speed dispersion. After the curing reaction was complete, the product was discharged at room temperature. After filtration, washing, and drying, the flake magnesium hydroxide flame retardant was obtained. The mass ratio of E20 epoxy resin, methyl methacrylate resin, ethylene glycol monobutyl ether, flake magnesium hydroxide flame retardant primary product, and diethylenetriamine is 20:1:500:150:2. The strong dispersion is uniform, with a dispersion rate of 8000 rpm and a dispersion time of 9 hours; The reaction temperature is 40°C; The low-speed dispersion has a dispersion rate of 1000 rpm; The curing reaction is complete, and the curing reaction time is 9 hours; The washing process involves washing three times with anhydrous ethanol, with the amount of anhydrous ethanol used each time being equal to the mass of the wet solid being washed. The drying process involves drying at 80°C for 13 hours.
[0016] Example 3: A method for preparing a flake-shaped magnesium hydroxide flame retardant Step 1: Precipitation synthesis Magnesium salt, pH buffer, morphology control agent, dispersant, and deionized water are placed in a reaction vessel and stirred until completely dissolved. The mixture is then heated to the reaction temperature and ammonia water is added dropwise under constant temperature and stirring. The dropping rate is controlled to stabilize the pH value of the reaction system at 10.3. After the addition is complete, stirring is continued until the reaction is complete. The mixture is then discharged, filtered, washed, and dried to obtain the initial product of flake magnesium hydroxide flame retardant. The magnesium salt is magnesium sulfate; The pH buffer is a mixture of 2,4,6-tris(aminohexanoic acid)-1,3,5-triazine and triethanolamine borate; The mass ratio of 2,4,6-tris(aminohexanoic acid)-1,3,5-triazine to triethanolamine borate is 37:45; The morphology control agent is a mixture of succinic dihydrazide and 2,3-dihydroxysuccinic dihydrazide in a mass ratio of 1:1. The dispersant is a mixture of sodium polymethacrylate and ammonium polymethacrylate in a mass ratio of 1:1. The mass concentration of the ammonia solution is 15 wt%. The mass ratio of the magnesium salt, pH buffer, morphology control agent, dispersant, deionized water, and ammonia is 115:11:10:6:880:540. The constant temperature stirring is carried out at a stirring rate of 1600 rpm; The reaction temperature is 65°C; Continue stirring until the reaction is complete, and the stirring reaction time is 2 hours; The washing process involves washing with deionized water until the pH of the washing solution reaches 7.8. The drying process involves drying at 110°C for 12 hours.
[0017] Step 2: Epoxy Coating E20 epoxy resin, methyl methacrylate resin, and ethylene glycol monobutyl ether were placed in a dispersion reactor and stirred until completely dissolved. Then, the initial product of flake magnesium hydroxide flame retardant was added and strongly dispersed evenly. The temperature was raised to the reaction temperature, and diethylenetriamine was added under low-speed dispersion. After the curing reaction was complete, the product was discharged at room temperature. After filtration, washing, and drying, the flake magnesium hydroxide flame retardant was obtained. The mass ratio of E20 epoxy resin, methyl methacrylate resin, ethylene glycol monobutyl ether, flake magnesium hydroxide flame retardant primary product, and diethylenetriamine is 80:10:1200:330:11. The strong dispersion is uniform, with a dispersion rate of 10,000 rpm and a dispersion time of 5 hours; The reaction temperature is 75°C; The low-speed dispersion has a dispersion rate of 2000 rpm; The curing reaction is complete, and the curing reaction time is 4 hours; The washing process involves washing five times with anhydrous ethanol, with the amount of anhydrous ethanol used each time being equal to the mass of the wet solid being washed. The drying process involves drying at 100°C for 6 hours.
[0018] Comparative Example 1: Based on Example 1, in step 1, the precipitation synthesis, no pH buffer was added; instead, 7 parts of pH buffer were replaced with 7 parts of deionized water. The specific operation is as follows: Step 1: Precipitation synthesis Replace 7 parts of pH buffer with 7 parts of deionized water, and perform the same other operations as in Example 1. Step 2 is the same as in Example 1.
[0019] Comparative Example 2: Based on Example 1, in step 1, the precipitation synthesis, no morphology control agent was added. Instead, 4 parts of morphology control agent were replaced with 4 parts of deionized water in equal amounts. The specific operation is as follows: Step 1: Precipitation synthesis Replace 4 parts of morphology control agent with 4 parts of deionized water in equal amounts, and perform the other operations as in Example 1; Step 2 is the same as in Example 1.
[0020] Comparative Example 3: Based on Example 1, in step 1, the precipitation synthesis, no dispersant was added, and 2 parts of dispersant were replaced with 2 parts of deionized water in equal amounts. The specific operation is as follows: Step 1: Precipitation synthesis Replace 2 parts of dispersant with 2 parts of deionized water in equal amounts, and perform the other operations as in Example 1; Step 2 is the same as in Example 1.
[0021] Comparative Example 4: Based on Example 1, without step 2 (epoxy coating), the flake magnesium hydroxide flame retardant was directly obtained by step 1 (precipitation method). The specific operation is as follows: Step 1: Precipitation synthesis Similar to Example 1, flake magnesium hydroxide flame retardant was obtained directly; Step 2, epoxy coating, is not performed.
[0022] Flame retardant performance and particle size distribution testing: Flame retardant performance was evaluated using EVA as the matrix resin. The flake magnesium hydroxide flame retardant obtained in Examples 1, 2, 3 and Comparative Examples 1, 2, 3, 4 was added to EVA at a mass fraction of 40 wt%. The mixing temperature was set at 130°C, the mixing time was set at 15 min, and the rotation speed was set at 50 r / min. After mixing, the mixture was pressed into sheets. The hot pressing temperature during the sheeting process was 135°C, the hot pressing time was 13 min, and the cold pressing time was 8 min. The resulting flake EVA material was then tested for flame retardant performance. The particle size of the flake magnesium hydroxide flame retardants obtained in Examples 1, 2, 3 and Comparative Examples 1, 2, 3, and 4 was tested using a laser particle size analyzer, and the D value was measured. 10 D 50 D 90 Comparative analysis of particle size was conducted using numerical values. The test results are shown in Table 1: Table 1 As can be seen from the data in Table 1, the flake magnesium hydroxide flame retardants obtained in Examples 1-3, when added to EVA at a mass fraction of 40 wt%, can all increase the oxygen index of EVA to above 31, and the UL94 vertical flammability rating can reach V-1. The particle size obtained from the laser particle size analyzer shows that the flake magnesium hydroxide flame retardants obtained in the three examples can be considered as submicron to nanometer-sized materials. This indicates that the present invention uses a precipitation synthesis method with relatively simple process conditions, combined with coating modification, to prepare flake magnesium hydroxide with submicron to nanometer-sized particles and excellent flame retardant properties. In Comparative Example 1, in step 1, the precipitation synthesis, no p was added. With pH buffer, the limiting oxygen index of EVA in Comparative Example 1 decreased to 23.7, the UL94 vertical flammability rating was lower than V-2, and the particle size also increased significantly. This indicates that the pH buffer has a significant impact on the growth of flake magnesium hydroxide by stabilizing the pH of the reaction system. The particle size comparison shows that the addition of the pH buffer can significantly reduce the particle size of flake magnesium hydroxide and improve flame retardant properties by reducing the particle size. In Comparative Example 2, no morphology control agent was added in step 1 and the precipitation synthesis. The limiting oxygen index of Comparative Example 2 decreased to 28.5, the UL94 vertical flammability rating decreased to V-2, and the particle size increased significantly. 50 Increased to 1.004 μm, from D 50 Numerically, it can be considered that the vast majority of flake magnesium hydroxide particles have reached the micrometer scale, indicating that the morphology control agent has a significant effect on regulating the particle size of flake magnesium hydroxide. In Comparative Example 3, no dispersant was added in step 1 and the precipitation method synthesis. The particle size of Comparative Example 3 increased dramatically to over the micrometer scale, and its D... 50 The particle size was as high as 5.698 μm, and the flame retardant performance also dropped drastically, with the limiting oxygen index reaching only 22.8% and the UL94 vertical flammability rating dropping below V-2. This indicates that the addition of dispersant plays a crucial role in the uniform dispersion of flake magnesium hydroxide. Without dispersant, severe agglomeration of flake magnesium hydroxide occurs, leading to a significant increase in particle size and a sharp decline in flame retardant performance. Comparative Example 4 did not undergo step 2 (epoxy coating) and directly obtained flake magnesium hydroxide flame retardant through step 1 (precipitation method). The particle size of Comparative Example 4 was slightly smaller than that of Example 1, indicating that epoxy coating slightly increases the particle size of flake magnesium hydroxide. However, the flame retardant performance of Comparative Example 4, with its smaller particle size, was far worse than that of Example 1. Both the limiting oxygen index and the UL94 vertical flammability rating dropped to the lowest values among all examples and comparative examples. This shows that flake magnesium hydroxide without epoxy coating is difficult to disperse uniformly in EVA matrix resin, and the agglomeration of flake magnesium hydroxide makes it difficult to achieve a flame retardant effect.
[0023] Appendix Figure 1 Appendix Figure 2 Appendix Figure 3 Appendix Figure 4The images shown are scanning electron microscope (SEM) images at 10,000x magnification of the following products: the primary product of the flake magnesium hydroxide flame retardant obtained in Example 1, the primary product of the flake magnesium hydroxide flame retardant obtained in Example 1, the primary product of the flake magnesium hydroxide flame retardant obtained in Comparative Example 1, and the primary product of the flake magnesium hydroxide flame retardant obtained in Comparative Example 2. Figure 1 As can be seen, the initial product of magnesium hydroxide flame retardant obtained after step 1 and precipitation synthesis in Example 1 has an approximately hexagonal flake morphology, with a thickness on the scale of a few nanometers and dimensions of tens to hundreds of nanometers in the length and width directions. It can be regarded as a nanomaterial in the one-dimensional thickness direction and as a nano to submicron-scale material in the three-dimensional length, width, and thickness directions. Figure 1 The flaky magnesium hydroxide in this invention does not exhibit large-sized agglomerated particles. Even the most severe agglomeration is limited to the stacking of several layers of flaky magnesium hydroxide. This indicates that the flaky magnesium hydroxide generated during the precipitation synthesis process is basically dispersed in the reaction system in a monolithic state. Therefore, the precipitation reaction system of this invention, composed of magnesium salt, pH buffer, morphology control agent, dispersant, deionized water, and ammonia, can effectively control the formation of magnesium hydroxide, maintaining a monodisperse, nearly hexagonal flaky morphology throughout the process. Moreover, the particle size growth is also under control at the micro-nano level. Figure 2 The magnesium hydroxide flame retardant in the film still exhibits a near-hexagonal flake shape with a thickness on the nanometer scale, but the hexagonal edges are no longer as sharp as... Figure 1 The edges of the flakes are not sharp and distinct, but rather rounded. This is likely due to the epoxy coating on the surface of the initial product of the flake magnesium hydroxide flame retardant. In addition, the thickness dimension of the epoxy-coated flake magnesium hydroxide is increased. This may be because during the coating process, it is difficult for the flake magnesium hydroxide to be dispersed into a single flake. Most of the coated flakes may be formed by stacking two or more hexagonal flake magnesium hydroxide flakes together and then epoxy coating them. Figure 3 The morphology of magnesium hydroxide in the medium is no longer flake-like, but rather presents as irregular, thick, blocky particles. Figure 3 As can be seen, these thick, blocky particles are mostly still at the nanometer to submicron scale in terms of length, width, and thickness. Figure 3 The corresponding Comparative Example 1, which does not contain a pH buffer, shows a particularly large decrease in flame retardant performance. Compared with Example 1, although the particle size of magnesium hydroxide obtained in Comparative Example 1 is not significantly increased, the morphology of its thick block particles does not provide good flame retardant performance. Compared with flake magnesium hydroxide, its flame retardant performance is obviously very poor. It can be seen that the addition of pH buffer plays a key role in the formation of flake morphology, and thus plays a crucial role in improving flame retardant performance. Figure 4 The initial sample of magnesium hydroxide flame retardant, while still in flake form, no longer exhibits a regular hexagonal shape. While the thickness has not increased significantly, the dimensions in both length and width planes have increased considerably, indicating a larger particle size. This may be the cause... Figure 4 One of the reasons why the flame retardant properties of Comparative Example 2 were significantly reduced was that no morphology control agent was added in Comparative Example 2. Figure 4 The flake-like magnesium hydroxide in the sample is difficult to form a regular hexagonal shape, indicating that the morphology control agent plays a key role in the formation of the regular hexagonal morphology.
[0024] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.
Claims
1. A method for preparing a flake-shaped magnesium hydroxide flame retardant, characterized in that: The preparation method of the flake magnesium hydroxide flame retardant includes two steps: precipitation synthesis and epoxy coating. The precipitation method involves placing magnesium salt, pH buffer, morphology control agent, dispersant, and deionized water into a reaction vessel, stirring until completely dissolved, heating to the reaction temperature, and adding ammonia water dropwise while maintaining a constant temperature and stirring. The dropwise addition rate is controlled to stabilize the pH value of the reaction system at 9.8~10.
3. After the addition is complete, stirring continues until the reaction is complete, and the product is discharged. After filtration, washing, and drying, the initial product of flake magnesium hydroxide flame retardant is obtained. The pH buffer is a mixture of 2,4,6-tris(aminohexanoic acid)-1,3,5-triazine and triethanolamine borate; The morphology control agent is one or a mixture of two of succinic dihydrazide and 2,3-dihydroxysuccinic dihydrazide in any mass ratio. The dispersant is one or a mixture of two of sodium polymethacrylate and ammonium polymethacrylate in any mass ratio; The epoxy coating process involves placing E20 epoxy resin, methyl methacrylated melamine resin, and ethylene glycol monobutyl ether into a dispersion reactor. After complete dissolution by stirring, the initial product of flake magnesium hydroxide flame retardant is added. After strong and uniform dispersion, the temperature is raised to the reaction temperature. Diethylenetriamine is added under low-speed dispersion. After the curing reaction is complete, the mixture is cooled to room temperature and discharged. After filtration, washing, and drying, the flake magnesium hydroxide flame retardant is obtained.
2. The method for preparing the flake magnesium hydroxide flame retardant according to claim 1, characterized in that: The magnesium salt is one or a mixture of any two or more of magnesium nitrate, magnesium chloride, and magnesium sulfate in any mass ratio.
3. The method for preparing the flake magnesium hydroxide flame retardant according to claim 1, characterized in that: The mass ratio of 2,4,6-tris(aminohexanoic acid)-1,3,5-triazine to triethanolamine borate is 13~37:
45.
4. The method for preparing the flake magnesium hydroxide flame retardant according to claim 1, characterized in that: The mass concentration of the ammonia solution is 6-15 wt%. The mass ratio of the magnesium salt, pH buffer, morphology control agent, dispersant, deionized water, and ammonia is 35~115:3~11:2~10:1~6:290~880:110~540.
5. The method for preparing the flake magnesium hydroxide flame retardant according to claim 1, characterized in that: The mass ratio of E20 epoxy resin, methyl methacrylated melamine resin, ethylene glycol monobutyl ether, flake magnesium hydroxide flame retardant precursor, and diethylenetriamine is 20~80:1~10:500~1200:150~330:2~11.