Spherical phosphonate flame retardant, its preparation method and application

Abstract

The application discloses a spherical phosphonate flame retardant and a preparation method and application thereof, and belongs to the technical field of high polymer materials. The preparation method of the spherical phosphonate flame retardant comprises the following steps: S1. preparing auxiliary stirring balls: mixing an alkyl hypophosphite aqueous solution and a flocculating agent, adding a soluble aluminum salt aqueous solution, filtering and washing to obtain the auxiliary stirring balls; S2. mixing and reacting the auxiliary stirring balls in S1, the alkyl hypophosphite aqueous solution and the soluble aluminum salt aqueous solution, and filtering to obtain the spherical phosphonate flame retardant. The spherical phosphonate flame retardant prepared by the application contains almost no impurities, has high product purity, can be extruded into a shape at a processing temperature of 340-360 DEG C together with high polymer materials, has a regular shape, has a crystal morphology close to a spherical shape, has a high tap density, and does not cause a pipe bridging problem when being blended with the high polymer materials.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and more specifically, to a spherical phosphonate flame retardant, its preparation method, and its application. Background Technology

[0002] Flame retardants are important additives used in polymer materials, capable of preventing or delaying their combustion. Organophosphorus flame retardants, as halogen-free flame retardants, possess advantages such as high flame retardant efficiency, low toxicity, low corrosivity, and good compatibility with polymer materials. Organic alkyl phosphinates are a novel type of organophosphorus flame retardant; flame-retardant products prepared by adding small amounts of organic alkyl phosphinates exhibit advantages such as low density, good mechanical properties, good color, and low smoke density.

[0003] Existing phosphonate flame retardants have irregular morphology, uneven particle size, and poor flowability, which makes them prone to problems such as pipe bridging when blended with polymer materials.

[0004] Existing technology discloses a method for preparing large-particle-size spherical dialkylphosphinate flame retardants. This method involves adding melamine compounds as seed crystals for precipitation reaction to dialkylphosphinates and adding surfactants to improve dispersion, resulting in spherical dialkylphosphinates with a particle size D50 of 30–70 μm. Although this phosphinate flame retardant also exhibits a spherical morphology, the addition of melamine cyanurate compounds during preparation reduces its purity and causes discoloration and decomposition at high temperatures. Furthermore, melamine cyanurate undergoes endothermic decomposition and sublimation above 300°C, reducing its flame-retardant effect and failing to maintain its spherical morphology. Therefore, this flame retardant can only be used for modifying polymeric resins (such as PBT or PP) that require extrusion molding at lower temperatures, and cannot be applied to modifying polymeric resins (such as high-temperature nylon PA10T) that require extrusion molding at processing temperatures above 340°C. Summary of the Invention

[0005] The technical problem this invention aims to solve is to overcome the defects and shortcomings of existing spherical phosphonate flame retardants, such as easy discoloration and decomposition at high temperatures and inability to be applied to the modification of polymer resins at 340-360℃. This invention provides a method for preparing spherical phosphonate flame retardants. The method involves mixing and reacting millimeter-sized stirring balls with aqueous solutions of alkyl phosphonates and soluble aluminum salts. The resulting spherical phosphonate flame retardant particles have a regular shape, a near-spherical morphology, high tap density, and good flowability. It avoids bridging issues when blended with polymer materials. Furthermore, it contains almost no impurities, resulting in high product purity and resistance to heat, yellowing, and high-temperature decomposition. This spherical phosphonate flame retardant can be used not only for the modification of polymer resins extruded at lower temperatures but also for the modification of polymer resins requiring extrusion at processing temperatures above 340℃ (such as high-temperature nylon PA10T).

[0006] Another object of the present invention is to provide a spherical phosphonate flame retardant.

[0007] Another object of the present invention is to provide an application of a spherical phosphonate flame retardant in the preparation of flame-retardant polymer materials.

[0008] The above-mentioned objective of this invention is achieved through the following technical solution:

[0009] A method for preparing a spherical phosphonate flame retardant includes the following steps:

[0010] S1. Preparation of stirring aid balls: Mix alkyl phosphonate aqueous solution and flocculant, stir, add soluble aluminum salt aqueous solution, filter, wash and dry to obtain stirring aid balls;

[0011] S2. Mix and stir the stirring ball from S1, the aqueous solution of the alkyl phosphonate, and the aqueous solution of the soluble aluminum salt. After filtration, washing, and drying, obtain a spherical phosphonate flame retardant.

[0012] In S1, the flocculant is an inorganic flocculant containing aluminum ions;

[0013] The average particle size of the stirring balls is 7–12 mm, and the average sphericity of the stirring balls is 0.7–1.

[0014] In S2, the reaction temperature is 20–80℃ and the reaction time is 0.1–3 h;

[0015] The mass ratio of the alkylphosphinate aqueous solution to the stirring ball is 1:(0.001~0.2).

[0016] It should be noted that:

[0017] In the preparation method of the spherical phosphonate flame retardant of the present invention, in step S1, a flocculant is first added and mixed with an aqueous solution of alkyl phosphonate and an aqueous solution of soluble aluminum salt to prepare stirring balls with a particle size of 7-12 mm. In step S2, the stirring balls with a larger particle size are used as powerful stirring balls to prepare spherical phosphonate flame retardants with regular shapes and high average sphericity.

[0018] Since the flocculant is an inorganic flocculant containing aluminum ions, and the alkyl phosphonates in S1 and S2 are the same as the soluble aluminum salt aqueous solution, no new impurity ions will be introduced into the system. The resulting spherical phosphonate flame retardant has high purity, high heat resistance, and is not prone to yellowing or decomposition.

[0019] The phosphonate flame retardant prepared by this invention has a large average sphericity, good flowability and uniform dispersion when extruded with polymer materials, and no pipeline bridging problem occurs when blended.

[0020] In S1, the average particle size of the stirring balls is too small, and within the same reaction time and temperature, the average sphericity of the obtained phosphonate flame retardant is significantly reduced.

[0021] In S1, if the average sphericity of the stirring balls is too small, the average sphericity of the generated phosphonate flame retardant will also be lower, resulting in irregular flame retardant morphology and low tap density, which will still lead to pipeline bridging problems.

[0022] In S2, if the amount of stirring balls added is too small, the crystal growth rate is slow, and the average sphericity of the obtained phosphonate flame retardant is significantly reduced.

[0023] In S1 and S2, the mass concentration of the alkylphosphonate aqueous solution can be 1% to 45%.

[0024] In S1 and S2, the mass concentration of the soluble aluminum salt aqueous solution can be 1%-39%.

[0025] In S1, the mass ratio of the alkylphosphinate aqueous solution to the flocculant can be 1:(0.001~0.01).

[0026] Preferably, in S1, the flocculant is one or more of polyaluminum sulfate, potassium aluminum sulfate, and polyaluminum chloride.

[0027] More preferably, the flocculant is polyaluminum sulfate or potassium aluminum sulfate.

[0028] In practical applications, soluble aluminum salts are usually aluminum sulfate salts, and flocculants are polyaluminum sulfate or potassium aluminum sulfate, which will not introduce impurities into the system.

[0029] Preferably, in S1, the mass ratio of the alkylphosphinate aqueous solution to the flocculant is 1:(0.002-0.003).

[0030] In S1, the mass ratio of the alkylphosphinate aqueous solution to the flocculant affects the growth rate of the stirring balls. If the mass of the flocculant relative to the alkylphosphinate aqueous solution is more than 0.003, the stirring balls will not grow further.

[0031] Preferably, in S2, the mass ratio of the alkylphosphinate aqueous solution to the stirring ball is 1:(0.01-0.02).

[0032] Preferably, in S1, the mixing temperature is 60-70°C and the mixing time is 12-15 hours.

[0033] Controlling the mixing temperature and mixing time in S1 can form stirring balls. Stirring balls with an average particle size of 7-12 mm can be obtained by screening or selection.

[0034] Preferably, in S2, the reaction temperature is 70–80°C and the reaction time is 1–2 h.

[0035] In S2, the reaction temperature and reaction time affect the shape of the phosphonate flame retardant. Controlling the reaction temperature to 70-80℃ and the reaction time to 1-2h can further improve the average sphericity of the phosphonate flame retardant.

[0036] Preferably, the alkyl phosphonate is one or more of diethyl phosphonate, sodium dipropyl phosphonate, ethyl phosphonate, butyl phosphonate, propyl phosphonite, or butyl phosphonite.

[0037] Alkylphosphonates can be sodium alkylphosphonates.

[0038] In practical applications, the soluble aluminum salt is aluminum sulfate.

[0039] This invention also protects the spherical phosphonate flame retardant prepared by the above-described method for preparing spherical phosphonate flame retardants.

[0040] The spherical phosphonate flame retardant prepared by this invention has excellent flame retardancy. Furthermore, during the mixing process with polymers, the spherical phosphonate flame retardant of this invention exhibits regular particle shape, a near-spherical morphology, high tap density, and good flowability. Therefore, when it is blended and modified with polymer materials, the feeding track is less prone to blockage or pipeline bridging. This invention particularly protects the application of the spherical phosphonate flame retardant in the preparation of flame-retardant polymer materials.

[0041] Preferably, in the application, the processing temperature is 340–360°C.

[0042] The spherical phosphonate flame retardant prepared by this invention contains almost no impurities, is heat-resistant and anti-yellowing, and can be melt-extruded with polymer materials at a relatively high processing temperature of 340-360°C, meeting the requirements of flame-retardant polymer materials with high processing temperature.

[0043] The polymer materials can be PBT, PA66 or PA6, as well as high-temperature nylon PA10T.

[0044] In practical applications, the processing temperature of high-temperature nylon resin is between 340 and 360°C. The phosphonate flame retardant of this invention will not decompose at high temperatures of 340 to 360°C, so it can be applied to the preparation of flame-retardant high-temperature nylon resin.

[0045] Compared with the prior art, the beneficial effects of the present invention are:

[0046] This invention discloses a method for preparing spherical phosphonate flame retardants. The method involves mixing and reacting millimeter-sized stirring balls with aqueous solutions of alkyl phosphonates and soluble aluminum salts. The resulting spherical phosphonate flame retardant particles have a regular shape, a near-spherical morphology, high tap density, and good flowability. It avoids bridging issues when blended with polymer materials. Furthermore, it is virtually free of impurities, exhibiting high purity, heat resistance, resistance to yellowing, and resistance to high-temperature decomposition. This method can be used not only for modifying polymer resins extruded at lower temperatures but also for modifying polymer resins requiring extrusion at processing temperatures above 340°C.

[0047] The spherical phosphonate flame retardant prepared by the method of the present invention has a particle size D50 of 35-45 μm, an average sphericity of 0.77-0.88, a tap density of 0.72-0.77 g / ml, and remains white after baking. The weight heat loss after baking does not exceed 1.54%.

[0048] The spherical phosphonate flame retardant of the present invention can be extruded not only with polymer resins at lower extrusion temperatures, but also with high-temperature nylon PA10T at processing temperatures above 340°C. Attached Figure Description

[0049] Figure 1 This is an electron scanning microscope image of the spherical phosphonate flame retardant in Example 1, magnified 100 times.

[0050] Figure 2 This is an electron scanning microscope image of the spherical phosphonate flame retardant from Example 1, magnified 400 times.

[0051] Figure 3 This is an electron scanning microscope image of the spherical phosphonate flame retardant from Example 1, magnified 1000 times.

[0052] Figure 4 The image shown is an electron scanning microscope image of the non-spherical phosphonate flame retardant in Comparative Example 1, magnified 100 times.

[0053] Figure 5 The image shows an electron scanning microscope image of the non-spherical phosphonate flame retardant in Comparative Example 1, magnified at 400x.

[0054] Figure 6 The image shown is an electron scanning microscope image of the non-spherical phosphonate flame retardant in Comparative Example 1, magnified 1000 times. Detailed Implementation

[0055] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0056] Example 1

[0057] A method for preparing a spherical phosphonate flame retardant includes the following steps:

[0058] S1. Preparation of stirring balls: Mix alkyl phosphonate aqueous solution and flocculant, add soluble aluminum salt aqueous solution, filter and wash to obtain stirring balls;

[0059] S2. Mix the stirring ball, alkyl phosphonate aqueous solution and soluble aluminum salt aqueous solution from S1, react them, filter, wash and dry at 160-260℃ to obtain spherical phosphonate flame retardant;

[0060] The alkylphosphonate aqueous solution is sodium diethylphosphonate aqueous solution, and the soluble aluminum salt is aluminum sulfate; the mass concentration of the alkylphosphonate aqueous solution is 26%, and the mass concentration of the soluble aluminum salt aqueous solution is 30%.

[0061] In S1, the flocculant is polyaluminum sulfate;

[0062] The mass ratio of the alkyl phosphonate aqueous solution to the flocculant is 1:0.002; the molar ratio of the alkyl phosphonate to the soluble aluminum salt is 6:1.

[0063] The mixing temperature was 70℃, and the mixing time was 15 hours.

[0064] Stirring balls with an average particle size of 10 mm and an average sphericity of 0.88 were selected.

[0065] In S2, the reaction temperature is 80℃ and the reaction time is 1 hour;

[0066] The mass ratio of the alkyl phosphonate aqueous solution to the stirring ball is 1:0.015; the molar ratio of the alkyl phosphonate to the soluble aluminum salt is 6:1.

[0067] Example 2

[0068] A method for preparing a spherical phosphonate flame retardant, which differs from Example 1, is as follows:

[0069] In S1, stirring balls with an average particle size of 12 mm are screened.

[0070] The rest is the same as in Example 1, and will not be repeated here.

[0071] Example 3

[0072] A method for preparing a spherical phosphonate flame retardant, which differs from Example 1, is as follows:

[0073] In S2, the mass ratio of the alkylphosphinate aqueous solution to the stirring ball is 1:0.2.

[0074] The rest is the same as in Example 1, and will not be repeated here.

[0075] Example 4

[0076] A method for preparing a spherical phosphonate flame retardant, which differs from Example 1, is as follows:

[0077] In S1, the mixing temperature is 70℃ and the mixing time is 10h.

[0078] Stirring balls with an average particle size of 7 mm and an average sphericity of 0.71 were selected.

[0079] The rest is the same as in Example 1, and will not be repeated here.

[0080] Example 5

[0081] A method for preparing a spherical phosphonate flame retardant, which differs from Example 1, is as follows:

[0082] In S2, the reaction temperature is 20℃ and the reaction time is 1h.

[0083] The rest is the same as in Example 1, and will not be repeated here.

[0084] Example 6

[0085] A method for preparing a spherical phosphonate flame retardant, which differs from Example 1, is as follows:

[0086] In S1, the mass ratio of the alkylphosphinate aqueous solution to the flocculant is 1:0.001.

[0087] The rest is the same as in Example 1, and will not be repeated here.

[0088] Comparative Example 1

[0089] A method for preparing a phosphonate flame retardant includes the following steps:

[0090] An aqueous solution of alkyl phosphonates and an aqueous solution of soluble aluminum salts were mixed and reacted, then filtered, washed, and dried at 160–260°C to obtain a phosphonate flame retardant.

[0091] Among them, the alkylphosphinate aqueous solution is sodium diethylphosphinate aqueous solution, and the soluble aluminum salt is aluminum sulfate aqueous solution;

[0092] The reaction temperature was 80℃, and the reaction time was 1 hour.

[0093] The molar ratio of alkylphosphinate to soluble aluminum salt is 6:1.

[0094] The difference from Example 1 is that the preparation of the S1 stirring ball is not included.

[0095] Comparative Example 2

[0096] A method for preparing a spherical phosphonate flame retardant, which differs from Example 1, is as follows:

[0097] In S1, the mixing temperature is 50℃ and the mixing time is 10h;

[0098] Stirring balls with an average particle size of 5 mm and an average sphericity of 0.88 were selected.

[0099] The rest is the same as in Example 1, and will not be repeated here.

[0100] Comparative Example 3

[0101] A method for preparing a spherical phosphonate flame retardant, which differs from Example 1, is as follows:

[0102] In S2, the mass ratio of the alkylphosphinate aqueous solution to the stirring ball is 1:0.0005.

[0103] The rest is the same as in Example 1, and will not be repeated here.

[0104] Comparative Example 4

[0105] A method for preparing a spherical phosphonate flame retardant, which differs from Example 1, is as follows:

[0106] In S1, the mixing temperature is 80℃ and the mixing time is 30h;

[0107] Stirring balls with an average particle size of 15 mm and an average sphericity of 0.88 were selected.

[0108] The rest is the same as in Example 1, and will not be repeated here.

[0109] Comparative Example 5

[0110] A method for preparing a spherical phosphonate flame retardant, which differs from Example 1, is as follows:

[0111] In S2, the mass ratio of the alkylphosphinate aqueous solution to the stirring ball is 1:0.3.

[0112] The rest is the same as in Example 1, and will not be repeated here.

[0113] Comparative Example 6

[0114] A method for preparing a spherical phosphonate flame retardant, which differs from Example 1, is as follows:

[0115] In S1, stirring balls with an average sphericity of 0.5 are selected.

[0116] The rest is the same as in Example 1, and will not be repeated here.

[0117] Result detection

[0118] The phosphonate flame retardants of Examples 1, 4, and 5 and Comparative Example 1 were mixed with PBT, glass fiber, and additives in a weight ratio of 10:50:30:10 and extruded from a twin-screw extruder at a processing temperature of 230–260°C to obtain flame-retardant thermoplastic polymer molding materials.

[0119] The phosphonate flame retardant of Examples 1, 4, and 5 and Comparative Example 1 were extruded with high-temperature nylon material PA10T and toughening agent at a weight ratio of 13.5:84:1.5, and the processing temperature was 340-360°C.

[0120] The spherical phosphonate flame retardants of the above embodiments and comparative examples, or the polymeric materials made from the above spherical phosphonate flame retardants, were all tested using the following performance testing methods:

[0121] Test method for average particle size of stirring balls: The average particle size of stirring balls is measured by vernier calipers. The average value is taken after three tests. The test standard is GB / T21389-2008.

[0122] Test method for average sphericity of stirring balls: Camsizer X2 particle size and shape analyzer.

[0123] Average sphericity of phosphonate flame retardants: particle size and shape analyzer Camsizer X2.

[0124] Particle size D50 of phosphonate flame retardants: The particle size of the flame retardant was determined by dispersing it in water using a laser particle size analyzer.

[0125] Tap density of phosphonate flame retardants: According to the powder tap density method: the test standard is GB / T21354-2008. The higher the tap density, the more regular the morphology of the flame retardant and the better its flowability.

[0126] Flame retardant yellowing test: Bake the flame retardant at 290℃ and normal pressure for 180 minutes and observe the color of the flame retardant. According to the RAL color chart, 9003 is signal white, 9016 is traffic white, 1001 is light yellow, and 1013 is light gray that is close to white. The colors change from white to yellow in the following order: 9003, 9016, 1013 and 1001.

[0127] Flame retardant heat loss test: After baking at 290℃ and normal pressure for 180 minutes, the weight loss was measured.

[0128] Flame retardant properties of polymer materials: tested according to the UL94-2018 standard method for flammability performance of plastics;

[0129] Mechanical properties of polymer materials:

[0130] Tensile strength: GB / T1040-1992 Test method for tensile properties of plastics;

[0131] Flexural strength: GB / T9341-2000 Test method for flexural properties of plastics;

[0132] Deflection: GB / T9341-2000 Test method for bending properties of plastics;

[0133] (10) Color: The resin is injection molded into a 2mm thick color plate and tested on a Color-Eye-7000A colorimeter (GretagMacbeth). The larger the L value, the whiter the color.

[0134] The specific test results are shown in Tables 1-3 below:

[0135] Table 1: Flame retardant performance tests of Examples 1-6 and Comparative Examples 1-6

[0136]

[0137]

[0138] Table 2: Performance Tests of PBT and Flame Retardant Modified Materials from Examples 1, 4, 5, and Comparative Example 1

[0139] Tensile strength (MPa) 117 113 115 108 Bending strength (MPa) 178 172 175 168 Deflection (mm) 4.3 4.1 4.1 3.8 UL94 flame retardancy 1.6mm V-0 V-0 V-0 V-1 UL94 flame retardancy 2.5mm V-0 V-0 V-0 V-0 Chromaticity L value 88 86 87 73

[0140] Table 3: Performance Tests of High-Temperature Nylon PA10T and Flame Retardant Modified Materials from Examples 1, 4, 5, and Comparative Example 1

[0141] Tensile strength (MPa) 150 146 145 139 Bending strength (MPa) 222 218 220 216 Deflection (mm) 4.2 4.0 4.1 3.8 UL94 flame retardancy 1.6mm V0 V0 V0 V1 UL94 flame retardancy 2.5mm V0 V0 V0 V0 Chromaticity L value 86 82 85 70

[0142] As can be seen from the above data, the spherical phosphonate flame retardant prepared by the method of the present invention has a particle size D50 of 35-45 μm, an average sphericity of 0.77-0.88, a tap density of 0.72-0.77 g / ml, and remains white after baking, with a weight heat loss of no more than 1.54% after baking.

[0143] As can be seen from Tables 2 and 3, the spherical phosphonate flame retardant of this invention can not only be used in the modification of polymer resins extruded at lower temperatures, but also in extrusion molding with high-temperature nylon PA10T at processing temperatures above 340°C. The spherical phosphonate flame retardant of this invention can improve the flame retardant properties of polymers, achieving a V0 rating. The spherical phosphonate flame retardant of this invention is heat-resistant and anti-yellowing, and blending it with polymers can also give the polymers higher whiteness.

[0144] From Example 1, Comparative Example 1 and Figures 1-6 As can be seen, in the preparation of phosphonate flame retardant in Comparative Example 1, without the addition of stirring balls, the phosphonate flame retardant prepared has an irregular morphology, uneven particle size, and a tap density of only 0.62 g / ml, with poor flowability. Therefore, it is prone to pipe bridging problems when blended with polymer materials.

[0145] As can be seen from Examples and Comparative Example 2, in S1, the average particle size of the stirring balls is too small, and within the same reaction time and temperature, the average sphericity of the obtained phosphonate flame retardant is significantly reduced.

[0146] As can be seen from Examples and Comparative Example 3, in S2, the amount of stirring balls added was too small, the crystal growth rate was slow, and the average sphericity of the obtained phosphonate flame retardant was significantly reduced.

[0147] As can be seen from Examples and Comparative Example 4, in S1, the average particle size of the stirring balls was too large, and the average sphericity of the obtained phosphonate flame retardant was significantly reduced.

[0148] As can be seen from Examples and Comparative Example 5, in S2, the amount of stirring balls added was too large, resulting in phosphate flame retardant particles with excessively large size, which are more easily decomposed during the processing of polymer materials.

[0149] As can be seen from Examples and Comparative Example 6, in S1, the average sphericity of the stirring balls is too low, and the average sphericity of the obtained phosphonate flame retardant is significantly reduced.

[0150] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a spherical phosphonate flame retardant, characterized in that, Includes the following steps: S1. Preparation of stirring balls: Mix alkyl phosphonate aqueous solution and flocculant, stir, add soluble aluminum salt aqueous solution, filter, wash and dry to obtain stirring balls; S2. The stirring ball from S1, the aqueous solution of the alkyl phosphinate, and the aqueous solution of the soluble aluminum salt are mixed and stirred to react. After filtration, washing, and drying, spherical phosphinate flame retardant is obtained. In S1, the flocculant is one or more of polyaluminum sulfate, potassium aluminum sulfate, or polyaluminum chloride; the mass ratio of alkylphosphinate aqueous solution to flocculant is 1:(0.002~0.003); the mixing temperature is 60~70℃, and the mixing time is 12~15h; The average particle size of the stirring balls is 7~12mm, and the average sphericity of the stirring balls is 0.7~1. In S2, the reaction temperature is 20~80℃ and the reaction time is 0.1~3h; The mass ratio of the alkylphosphinic acid aqueous solution to the stirring ball is 1:(0.001~0.2).

2. The method for preparing the spherical phosphonate flame retardant as described in claim 1, characterized in that, In S2, the mass ratio of the alkylphosphinic acid aqueous solution to the stirring ball is 1:(0.01~0.02).

3. The method for preparing the spherical phosphonate flame retardant as described in claim 1, characterized in that, In S2, the reaction temperature is 70~80℃ and the reaction time is 1~2h.

4. The method for preparing the spherical phosphonate flame retardant as described in claim 1, characterized in that, The alkyl phosphonate is one or more of diethyl phosphonate, sodium dipropyl phosphonate, ethyl phosphonate, and butyl phosphonate.

5. The method for preparing the spherical phosphonate flame retardant as described in claim 1, characterized in that, The soluble aluminum salt is aluminum sulfate.

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